Bug 972577: Consolidate IOInterposer initialization code; r=froydnj,BenWa,jimm

--HG--
rename : tools/profiler/IOInterposer.cpp => xpcom/build/IOInterposer.cpp
rename : tools/profiler/IOInterposer.h => xpcom/build/IOInterposer.h
rename : tools/profiler/NSPRInterposer.cpp => xpcom/build/NSPRInterposer.cpp
rename : tools/profiler/NSPRInterposer.h => xpcom/build/NSPRInterposer.h
rename : toolkit/xre/nsWindowsDllInterceptor.h => xpcom/build/nsWindowsDllInterceptor.h