Back out JS-as-C++, because it's a suspect in the Linux performance regression.

--HG--
rename : js/src/js.cpp => js/src/js.c
rename : js/src/jsapi.cpp => js/src/jsapi.c
rename : js/src/jsarena.cpp => js/src/jsarena.c
rename : js/src/jsarray.cpp => js/src/jsarray.c
rename : js/src/jsatom.cpp => js/src/jsatom.c
rename : js/src/jsbool.cpp => js/src/jsbool.c
rename : js/src/jscntxt.cpp => js/src/jscntxt.c
rename : js/src/jscpucfg.cpp => js/src/jscpucfg.c
rename : js/src/jsdate.cpp => js/src/jsdate.c
rename : js/src/jsdbgapi.cpp => js/src/jsdbgapi.c
rename : js/src/jsdhash.cpp => js/src/jsdhash.c
rename : js/src/jsdtoa.cpp => js/src/jsdtoa.c
rename : js/src/jsemit.cpp => js/src/jsemit.c
rename : js/src/jsexn.cpp => js/src/jsexn.c
rename : js/src/jsfile.cpp => js/src/jsfile.c
rename : js/src/jsfun.cpp => js/src/jsfun.c
rename : js/src/jsgc.cpp => js/src/jsgc.c
rename : js/src/jshash.cpp => js/src/jshash.c
rename : js/src/jsinterp.cpp => js/src/jsinterp.c
rename : js/src/jsinvoke.cpp => js/src/jsinvoke.c
rename : js/src/jsiter.cpp => js/src/jsiter.c
rename : js/src/jskwgen.cpp => js/src/jskwgen.c
rename : js/src/jslock.cpp => js/src/jslock.c
rename : js/src/jslog2.cpp => js/src/jslog2.c
rename : js/src/jslong.cpp => js/src/jslong.c
rename : js/src/jsmath.cpp => js/src/jsmath.c
rename : js/src/jsnum.cpp => js/src/jsnum.c
rename : js/src/jsobj.cpp => js/src/jsobj.c
rename : js/src/jsopcode.cpp => js/src/jsopcode.c
rename : js/src/jsparse.cpp => js/src/jsparse.c
rename : js/src/jsprf.cpp => js/src/jsprf.c
rename : js/src/jsregexp.cpp => js/src/jsregexp.c
rename : js/src/jsscan.cpp => js/src/jsscan.c
rename : js/src/jsscope.cpp => js/src/jsscope.c
rename : js/src/jsscript.cpp => js/src/jsscript.c
rename : js/src/jsstr.cpp => js/src/jsstr.c
rename : js/src/jsutil.cpp => js/src/jsutil.c
rename : js/src/jsxdrapi.cpp => js/src/jsxdrapi.c
rename : js/src/jsxml.cpp => js/src/jsxml.c
rename : js/src/prmjtime.cpp => js/src/prmjtime.c