Bug 843907 - Move to manual barriering for MapObject and SetObject's key; r=billm

Automatically adding keys from the OrderedHashTable to the store buffer does not
work because the table uses a non-null value to indicate "empty". Since
RelocatableValue expects NULL to be used for this purpose, minor GCs attempt to
mark the tombstone as if it were a value. This obviously fails.

RelocatableValue is also extremely slow and moving to manual barriering will
make MapObject and SetObject faster with generational GC.

--HG--
rename : content/svg/content/src/SVGFETileElement.cpp => content/svg/content/src/nsSVGFilters.cpp
extra : rebase_source : ae675d0a16c61fccb7a88468cd32ae2d1899e2e3