Enhancements to BSONObjBuilder family of classes' stream API

Conflicts:

	src/mongo/bson/bsonobjbuilder.h
Fix compile
Merge branch 'aggcherrypick' into command-cursors

Conflicts:
	src/mongo/base/string_data.h
	src/mongo/bson/bsonobjbuilder.h
	src/mongo/dbtests/jsobjtests.cpp