Fix default queue name prefix delimiter
Fix default queue name prefix delimiter

Now displays as underscore, and not an empty string, when converted from markdown to HTML.
Escaped the underscore per http://daringfireball.net/projects/markdown/syntax#em
Fixes rails/rails#18009
Erol/rails,illacceptanything/illacceptanything,felipecvo/rails,sealocal/rails,lcreid/rails,lucasmazza/rails,shioyama/rails,illacceptanything/illacceptanything,yawboakye/rails,gcourtemanche/rails,iainbeeston/rails,xlymian/rails,joonyou/rails,mechanicles/rails,ttanimichi/rails,flanger001/rails,aditya-kapoor/rails,rafaelfranca/omg-rails,kamipo/rails,esparta/rails,hanystudy/rails,Vasfed/rails,MSP-Greg/rails,kamipo/rails,elfassy/rails,richseviora/rails,betesh/rails,stefanmb/rails,untidy-hair/rails,stefanmb/rails,Edouard-chin/rails,repinel/rails,eileencodes/rails,MichaelSp/rails,notapatch/rails,brchristian/rails,samphilipd/rails,koic/rails,eileencodes/rails,BlakeWilliams/rails,fabianoleittes/rails,kmcphillips/rails,mtsmfm/railstest,palkan/rails,pschambacher/rails,esparta/rails,rails/rails,flanger001/rails,coreyward/rails,kddeisz/rails,illacceptanything/illacceptanything,yalab/rails,odedniv/rails,bogdanvlviv/rails,gfvcastro/rails,assain/rails,Vasfed/rails,kaspth/rails,jeremy/rails,yalab/rails,riseshia/railsguides.kr,betesh/rails,Sen-Zhang/rails,vassilevsky/rails,yasslab/railsguides.jp,Edouard-chin/rails,arunagw/rails,matrinox/rails,travisofthenorth/rails,yhirano55/rails,riseshia/railsguides.kr,illacceptanything/illacceptanything,baerjam/rails,rafaelfranca/omg-rails,mijoharas/rails,lucasmazza/rails,xlymian/rails,mohitnatoo/rails,fabianoleittes/rails,mechanicles/rails,notapatch/rails,yasslab/railsguides.jp,eileencodes/rails,gauravtiwari/rails,starknx/rails,illacceptanything/illacceptanything,kddeisz/rails,kirs/rails-1,travisofthenorth/rails,kachick/rails,Envek/rails,vipulnsward/rails,EmmaB/rails-1,alecspopa/rails,palkan/rails,kirs/rails-1,gavingmiller/rails,gfvcastro/rails,illacceptanything/illacceptanything,utilum/rails,georgeclaghorn/rails,sealocal/rails,tgxworld/rails,pvalena/rails,tgxworld/rails,Stellenticket/rails,schuetzm/rails,pvalena/rails,MichaelSp/rails,kachick/rails,odedniv/rails,bradleypriest/rails,mathieujobin/reduced-rails-for-travis,mtsmfm/rails,sergey-alekseev/rails,Erol/rails,sergey-alekseev/rails,ttanimichi/rails,ngpestelos/rails,kamipo/rails,coreyward/rails,deraru/rails,arunagw/rails,rbhitchcock/rails,bolek/rails,jeremy/rails,mathieujobin/reduced-rails-for-travis,fabianoleittes/rails,vassilevsky/rails,shioyama/rails,alecspopa/rails,aditya-kapoor/rails,gfvcastro/rails,mtsmfm/railstest,deraru/rails,tgxworld/rails,Spin42/rails,eileencodes/rails,illacceptanything/illacceptanything,yahonda/rails,mathieujobin/reduced-rails-for-travis,prathamesh-sonpatki/rails,BlakeWilliams/rails,assain/rails,gauravtiwari/rails,mijoharas/rails,aditya-kapoor/rails,bogdanvlviv/rails,schuetzm/rails,koic/rails,prathamesh-sonpatki/rails,BlakeWilliams/rails,deraru/rails,samphilipd/rails,brchristian/rails,baerjam/rails,arjes/rails,tijwelch/rails,prathamesh-sonpatki/rails,ttanimichi/rails,ledestin/rails,printercu/rails,kenta-s/rails,kenta-s/rails,pvalena/rails,lcreid/rails,elfassy/rails,mohitnatoo/rails,kmcphillips/rails,arjes/rails,iainbeeston/rails,Stellenticket/rails,EmmaB/rails-1,printercu/rails,assain/rails,Stellenticket/rails,illacceptanything/illacceptanything,hanystudy/rails,alecspopa/rails,untidy-hair/rails,gcourtemanche/rails,repinel/rails,esparta/rails,gavingmiller/rails,bogdanvlviv/rails,yahonda/rails,Edouard-chin/rails,maicher/rails,tjschuck/rails,Envek/rails,illacceptanything/illacceptanything,kaspth/rails,arunagw/rails,yawboakye/rails,gfvcastro/rails,tjschuck/rails,Edouard-chin/rails,kmayer/rails,yalab/rails,kenta-s/rails,MSP-Greg/rails,yawboakye/rails,amoody2108/TechForJustice,amoody2108/TechForJustice,voray/rails,tjschuck/rails,deraru/rails,MSP-Greg/rails,mijoharas/rails,vipulnsward/rails,Vasfed/rails,palkan/rails,bradleypriest/rails,marklocklear/rails,koic/rails,georgeclaghorn/rails,mohitnatoo/rails,yahonda/rails,rails/rails,esparta/rails,tgxworld/rails,BlakeWilliams/rails,flanger001/rails,yhirano55/rails,lcreid/rails,kaspth/rails,vipulnsward/rails,starknx/rails,illacceptanything/illacceptanything,iainbeeston/rails,utilum/rails,palkan/rails,matrinox/rails,88rabbit/newRails,felipecvo/rails,shioyama/rails,marklocklear/rails,MichaelSp/rails,hanystudy/rails,amoody2108/TechForJustice,ngpestelos/rails,voray/rails,Spin42/rails,schuetzm/rails,felipecvo/rails,printercu/rails,assain/rails,tijwelch/rails,kmcphillips/rails,bolek/rails,rossta/rails,EmmaB/rails-1,Envek/rails,illacceptanything/illacceptanything,stefanmb/rails,rails/rails,georgeclaghorn/rails,brchristian/rails,prathamesh-sonpatki/rails,Stellenticket/rails,Sen-Zhang/rails,mechanicles/rails,jeremy/rails,yhirano55/rails,repinel/rails,fabianoleittes/rails,illacceptanything/illacceptanything,joonyou/rails,aditya-kapoor/rails,travisofthenorth/rails,kmayer/rails,bolek/rails,vassilevsky/rails,mtsmfm/rails,betesh/rails,illacceptanything/illacceptanything,coreyward/rails,ledestin/rails,riseshia/railsguides.kr,baerjam/rails,voray/rails,gcourtemanche/rails,vipulnsward/rails,riseshia/railsguides.kr,gauravtiwari/rails,kmayer/rails,mohitnatoo/rails,illacceptanything/illacceptanything,notapatch/rails,marklocklear/rails,matrinox/rails,88rabbit/newRails,88rabbit/newRails,utilum/rails,sealocal/rails,rails/rails,schuetzm/rails,xlymian/rails,yahonda/rails,rbhitchcock/rails,maicher/rails,ngpestelos/rails,iainbeeston/rails,richseviora/rails,samphilipd/rails,yalab/rails,MSP-Greg/rails,elfassy/rails,kmcphillips/rails,gavingmiller/rails,rafaelfranca/omg-rails,utilum/rails,yasslab/railsguides.jp,untidy-hair/rails,Sen-Zhang/rails,rossta/rails,repinel/rails,yawboakye/rails,mtsmfm/railstest,richseviora/rails,lucasmazza/rails,Vasfed/rails,starknx/rails,tjschuck/rails,rossta/rails,kddeisz/rails,travisofthenorth/rails,kachick/rails,Erol/rails,mtsmfm/rails,betesh/rails,tijwelch/rails,kddeisz/rails,pschambacher/rails,illacceptanything/illacceptanything,mechanicles/rails,Spin42/rails,arjes/rails,lcreid/rails,joonyou/rails,ledestin/rails,flanger001/rails,Envek/rails,printercu/rails,notapatch/rails,pschambacher/rails,baerjam/rails,yhirano55/rails,yasslab/railsguides.jp,rbhitchcock/rails,pvalena/rails,jeremy/rails,maicher/rails,joonyou/rails,odedniv/rails,bradleypriest/rails,sergey-alekseev/rails,georgeclaghorn/rails,Erol/rails,shioyama/rails,bogdanvlviv/rails,untidy-hair/rails,kirs/rails-1,arunagw/rails