Bug 1043554 - remove redundant social/ {Makefile,moz.build}; r=mshal

XPCSHELL_RESOURCES seems to be leftover from pre-manifest days, and the
manifest already has everything we need.
Bug 1043957 - remove some libs:: rules from devtools's Makefile.ins; r=mshal
Bug 1044046 - remove toolkit/components/workerloader/Makefile.in; r=mshal
Bug 1044047 - add EXTRA_JS_MODULES to _MOZBUILD_EXTERNAL_VARIABLES; r=mshal
Bug 1044041 - remove now-unnecessary rule from services/healthreport/Makefile.in; r=gps
Bug 1044165 - fix BuildReaderError exception printing to cope properly with SyntaxError; r=gps

Some moz.build syntax errors cause the thrown SyntaxError object to not include
an offset field, leading to all sorts of hilarity when we try printing messages
depending on SyntaxError.offset.  Check for this case and simply don't print
the caret if so.