Bug 853071: add some build-time defines for channel-specific features, r=gps, f=bhearsum

--HG--
rename : browser/config/mozconfigs/linux32/release => browser/config/mozconfigs/linux32/beta
rename : browser/config/mozconfigs/linux64/release => browser/config/mozconfigs/linux64/beta
rename : browser/config/mozconfigs/macosx-universal/release => browser/config/mozconfigs/macosx-universal/beta
rename : browser/config/mozconfigs/win32/release => browser/config/mozconfigs/win32/beta
extra : transplant_source : %F6%CFK%CE%16v%07%8A%D5o%97%8C%BB%95q%D5%3C%93%2B%94