Bug 891088 - Rename nsXBLChildrenElement -> mozilla::dom::XBLChildrenElement. r=peterv

--HG--
rename : content/xbl/src/nsXBLChildrenElement.cpp => content/xbl/src/XBLChildrenElement.cpp
rename : content/xbl/src/nsXBLChildrenElement.h => content/xbl/src/XBLChildrenElement.h