Revert some ActiveSupport::Callbacks changes.
Revert some ActiveSupport::Callbacks changes.

This reverts commits 911a0859ac065aa8e8834ac985353d659c7c7b65 and
30b31f51af6f7094c4a27b086755fc66c368d6fa.

Reason: these changes make the Active Model tests fail randomly.

Some examples:
http://travis-ci.org/#!/rails/rails/jobs/1498992
http://travis-ci.org/#!/rails/rails/jobs/1496948
http://travis-ci.org/#!/rails/rails/jobs/1489985

This script was used to reproduce these breaks:
https://gist.github.com/f6828a03ee4d40bffbc3

200 times, 0 failures

gcourtemanche/rails,mohitnatoo/rails,rails/rails,repinel/rails,palkan/rails,Stellenticket/rails,tijwelch/rails,mijoharas/rails,prathamesh-sonpatki/rails,odedniv/rails,georgeclaghorn/rails,travisofthenorth/rails,illacceptanything/illacceptanything,vassilevsky/rails,jeremy/rails,Spin42/rails,kamipo/rails,Edouard-chin/rails,tijwelch/rails,ttanimichi/rails,iainbeeston/rails,eileencodes/rails,marklocklear/rails,Stellenticket/rails,ngpestelos/rails,deraru/rails,kaspth/rails,BlakeWilliams/rails,joonyou/rails,kmayer/rails,yawboakye/rails,brchristian/rails,aditya-kapoor/rails,mtsmfm/rails,vassilevsky/rails,shioyama/rails,voray/rails,odedniv/rails,voray/rails,gavingmiller/rails,shioyama/rails,mtsmfm/rails,jeremy/rails,ledestin/rails,kddeisz/rails,shioyama/rails,alecspopa/rails,stefanmb/rails,kenta-s/rails,mohitnatoo/rails,georgeclaghorn/rails,yahonda/rails,gfvcastro/rails,samphilipd/rails,fabianoleittes/rails,Sen-Zhang/rails,illacceptanything/illacceptanything,notapatch/rails,kmayer/rails,arunagw/rails,EmmaB/rails-1,schuetzm/rails,mechanicles/rails,utilum/rails,brchristian/rails,kmcphillips/rails,riseshia/railsguides.kr,lucasmazza/rails,utilum/rails,repinel/rails,mathieujobin/reduced-rails-for-travis,shioyama/rails,rails/rails,betesh/rails,betesh/rails,alecspopa/rails,rossta/rails,assain/rails,elfassy/rails,mechanicles/rails,flanger001/rails,EmmaB/rails-1,ngpestelos/rails,Envek/rails,pvalena/rails,arunagw/rails,deraru/rails,illacceptanything/illacceptanything,amoody2108/TechForJustice,printercu/rails,arjes/rails,matrinox/rails,kddeisz/rails,illacceptanything/illacceptanything,schuetzm/rails,illacceptanything/illacceptanything,pvalena/rails,illacceptanything/illacceptanything,mathieujobin/reduced-rails-for-travis,felipecvo/rails,untidy-hair/rails,esparta/rails,sealocal/rails,bogdanvlviv/rails,odedniv/rails,rbhitchcock/rails,Vasfed/rails,kamipo/rails,prathamesh-sonpatki/rails,koic/rails,mechanicles/rails,utilum/rails,jeremy/rails,tgxworld/rails,yasslab/railsguides.jp,kenta-s/rails,aditya-kapoor/rails,vipulnsward/rails,yhirano55/rails,tjschuck/rails,kenta-s/rails,kirs/rails-1,88rabbit/newRails,tjschuck/rails,starknx/rails,esparta/rails,illacceptanything/illacceptanything,coreyward/rails,elfassy/rails,yawboakye/rails,mathieujobin/reduced-rails-for-travis,yalab/rails,hanystudy/rails,joonyou/rails,lcreid/rails,lcreid/rails,pschambacher/rails,elfassy/rails,kmcphillips/rails,yasslab/railsguides.jp,pvalena/rails,matrinox/rails,sealocal/rails,pvalena/rails,rafaelfranca/omg-rails,printercu/rails,kaspth/rails,gfvcastro/rails,baerjam/rails,Envek/rails,rafaelfranca/omg-rails,arjes/rails,tgxworld/rails,Vasfed/rails,arjes/rails,ledestin/rails,BlakeWilliams/rails,assain/rails,sergey-alekseev/rails,marklocklear/rails,repinel/rails,yalab/rails,Edouard-chin/rails,travisofthenorth/rails,vipulnsward/rails,yasslab/railsguides.jp,Stellenticket/rails,aditya-kapoor/rails,lucasmazza/rails,richseviora/rails,rbhitchcock/rails,gauravtiwari/rails,notapatch/rails,flanger001/rails,MSP-Greg/rails,kachick/rails,illacceptanything/illacceptanything,ttanimichi/rails,yasslab/railsguides.jp,gfvcastro/rails,yawboakye/rails,utilum/rails,Vasfed/rails,joonyou/rails,mijoharas/rails,voray/rails,esparta/rails,aditya-kapoor/rails,baerjam/rails,MSP-Greg/rails,Erol/rails,coreyward/rails,iainbeeston/rails,samphilipd/rails,kmayer/rails,Envek/rails,gauravtiwari/rails,Envek/rails,gauravtiwari/rails,bradleypriest/rails,georgeclaghorn/rails,illacceptanything/illacceptanything,88rabbit/newRails,tjschuck/rails,lucasmazza/rails,Sen-Zhang/rails,BlakeWilliams/rails,eileencodes/rails,88rabbit/newRails,prathamesh-sonpatki/rails,notapatch/rails,illacceptanything/illacceptanything,MichaelSp/rails,ledestin/rails,gcourtemanche/rails,fabianoleittes/rails,Erol/rails,palkan/rails,sergey-alekseev/rails,vassilevsky/rails,Stellenticket/rails,joonyou/rails,mechanicles/rails,Edouard-chin/rails,palkan/rails,bolek/rails,koic/rails,riseshia/railsguides.kr,bogdanvlviv/rails,ttanimichi/rails,illacceptanything/illacceptanything,vipulnsward/rails,kmcphillips/rails,BlakeWilliams/rails,coreyward/rails,MichaelSp/rails,assain/rails,EmmaB/rails-1,amoody2108/TechForJustice,schuetzm/rails,koic/rails,rossta/rails,gcourtemanche/rails,pschambacher/rails,jeremy/rails,rossta/rails,felipecvo/rails,alecspopa/rails,samphilipd/rails,pschambacher/rails,yawboakye/rails,tjschuck/rails,sealocal/rails,matrinox/rails,kachick/rails,maicher/rails,Spin42/rails,baerjam/rails,tgxworld/rails,deraru/rails,kddeisz/rails,yahonda/rails,kmcphillips/rails,yhirano55/rails,kddeisz/rails,palkan/rails,illacceptanything/illacceptanything,bradleypriest/rails,MichaelSp/rails,georgeclaghorn/rails,flanger001/rails,hanystudy/rails,mtsmfm/railstest,mohitnatoo/rails,mtsmfm/rails,gavingmiller/rails,starknx/rails,MSP-Greg/rails,kirs/rails-1,bogdanvlviv/rails,illacceptanything/illacceptanything,printercu/rails,travisofthenorth/rails,riseshia/railsguides.kr,Vasfed/rails,xlymian/rails,Spin42/rails,deraru/rails,marklocklear/rails,gavingmiller/rails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