This should finally fix the ref leaks that keep all gecko nsDocuments alive even on the most basic docs.
-- v2: mshtml/tests: Fix element leak in elem_fire_event. mshtml: Pass actual node_ccp to ccref_decr for nodes. mshtml: Fix nsChannel's load_info leak. mshtml: Support cycle collection for nsChannel. mshtml: Ensure SnowWhite objects are cleared when forcing cycle collection. mshtml: Supply dummy logger when forcing cycle collection. mshtml: Flush all gecko thread events after detaching Gecko browser. mshtml: Fix nsProgressEvent leak for pre IE10 modes. mshtml: Fix URI leak in NewURI on failure. mshtml: Fix nsIFile dir leak in init_xpcom. mshtml: Fix factory leak in init_nsio. mshtml: Do not release the principal returned by GetPrincipal.