SERVER-9713 Port some BSONObj accessors to accept StringData

Accessors ported:
- getIntField
- getBoolField
- getStringField
- getObjectField
- operator[]
- getFieldUsingIndexNames
SERVER-9713 Rewrite BSONObj::getFieldDotted to accept StringData

Conflicts:
	src/mongo/dbtests/jsobjtests.cpp
Merge branch 'cp/9713'