Split message and stack into two separate variables
Split message and stack into two separate variables

This refactoring is to first step towards supporting error.htmlMessage.
We restructured the code to have a variable for the error message and
the error stack. This will allow us to use error.htmlMessage instead of
error.message as the message displayed to the user. The next commit will
take advantage of this separation.

GranitB/mocha,tswaters/mocha,menelaos/mocha-solarized,charlie77/mocha,kolodny/mocha,rlugojr/mocha,woodyrew/mocha,ELLIOTTCABLE/mocha,gaye/mocha,Shyp/mocha,mochajs/mocha,geometrybase/mocha,luxe-eng/valet-express.mocha,geometrybase/mocha,irnc/mocha,ELLIOTTCABLE/mocha,sul4bh/mocha,igwejk/mocha,nexdrew/mocha,ajaykodali/mocha,sul4bh/mocha,nexdrew/mocha,boneskull/mocha,mponizil/mocha,upfrontIO/mocha,GabrielNicolasAvellaneda/mocha,rlugojr/mocha,jbnicolai/mocha,tinganho/mocha,kevinburke/mocha,menelaos/mocha-solarized,beatfactor/mocha,phated/mocha,GerHobbelt/mocha,jjoos/mocha,jbnicolai/mocha,verkkokauppacom/mocha,upfrontIO/mocha,mochajs/mocha,luxe-eng/valet-express.mocha,antoval/mocha,mysterycommand/mocha,mbovel/mocha,ryanshawty/mocha,adamgruber/mocha,KevinTCoughlin/mocha,Khan/mocha,luxe-eng/valet-express.mocha,nightwatchjs/mocha-nightwatch,wltsmrz/mocha,JohnnyEstilles/mocha,tswaters/mocha,aaroncrows/mocha,ELLIOTTCABLE/mocha,ryanshawty/mocha,JohnnyEstilles/mocha,beni55/mocha,Shyp/mocha,santiagoaguiar/mocha,nightwatchjs/mocha-nightwatch,phated/mocha,mysterycommand/mocha,imsobear/mocha,IveWong/mocha,node-rookie/mocha,Shyp/mocha,pumpupapp/mocha,apkiernan/mocha,hoverduck/mocha,Phoenixmatrix/mocha,gaye/mocha,woodyrew/mocha,moander/mocha,mochajs/mocha,jjoos/mocha,santiagoaguiar/mocha,rlugojr/mocha,ajaykodali/mocha,jasonkarns/mocha,node-rookie/mocha,joshski/mocha,gaye/mocha,tinganho/mocha,ryanshawty/mocha,antoval/mocha,antoval/mocha,boneskull/mocha,igwejk/mocha,mbovel/mocha,sul4bh/mocha,Khan/mocha,hoverduck/mocha,outsideris/mocha,villesau/mocha,aaroncrows/mocha,woodyrew/mocha,hashcube/mocha,IveWong/mocha,joshski/mocha,villesau/mocha,imsobear/mocha,charlie77/mocha,kyroskoh/mocha,youprofit/mocha,hashcube/mocha,kevinburke/mocha,charlie77/mocha,cleberar38/mocha,GranitB/mocha,tswaters/mocha,DeNA/mocha,mysterycommand/mocha,GabrielNicolasAvellaneda/mocha,jkresner/mocha,irnc/mocha,hoverduck/mocha,aaroncrows/mocha,GerHobbelt/mocha,adamgruber/mocha,beni55/mocha,jkresner/mocha,wltsmrz/mocha,node-rookie/mocha,Hacker0x01/mocha,villesau/mocha,beatfactor/mocha,cleberar38/mocha,upfrontIO/mocha,Khan/mocha,youprofit/mocha,apkiernan/mocha,menelaos/mocha-solarized,kolodny/mocha,mbovel/mocha,hoverduck/mocha,outsideris/mocha,GabrielNicolasAvellaneda/mocha,IveWong/mocha,kyroskoh/mocha,Phoenixmatrix/mocha,KevinTCoughlin/mocha,mponizil/mocha,beni55/mocha,mponizil/mocha,jasonkarns/mocha,DeNA/mocha,joshski/mocha,santiagoaguiar/mocha,irnc/mocha,JohnnyEstilles/mocha,GranitB/mocha,phated/mocha,Hacker0x01/mocha,DeNA/mocha,verkkokauppacom/mocha,netei/mocha,wltsmrz/mocha,KevinTCoughlin/mocha,ajaykodali/mocha,GerHobbelt/mocha,Phoenixmatrix/mocha,youprofit/mocha,verkkokauppacom/mocha,jbnicolai/mocha,pumpupapp/mocha,beatfactor/mocha,pumpupapp/mocha,jjoos/mocha,moander/mocha,geometrybase/mocha,boneskull/mocha,apkiernan/mocha,Hacker0x01/mocha,jasonkarns/mocha,kevinburke/mocha,hashcube/mocha,moander/mocha,nexdrew/mocha,tinganho/mocha,kolodny/mocha,nightwatchjs/mocha-nightwatch,cleberar38/mocha,kyroskoh/mocha,imsobear/mocha,netei/mocha,netei/mocha,adamgruber/mocha,jkresner/mocha