Bug 996798 patch 2 - Make the ability to change nsWrapperCache::FlagsType more portable.  r=bzbarsky

Without this, an Android build on our automation gives:
content/xul/content/src/nsXULElement.h:359:117: error: left shift count >= width of type [-Werror]
Bug 1031635 - Add --debugger-args option to reftest mach commands.  r=gps

This allows useful argument combinations such as:
  --debugger valgrind
  --debugger-args "--tool=memcheck --leak-check=no --trace-children=yes --num-callers=50"