Added SafeNum type SERVER-6399

Conflicts:
	src/mongo/SConscript
Add SafeNum::isValid
Adding mutable bson classes

Conflicts:
	src/mongo/SConscript
	src/mongo/base/error_codes.err
Fixed lint warning and windows/linux32 compilation.
SERVER-7172 Make mutablebson's find const
SERVER-7172 Fix type
SERVER-7172 Fix mutablebson timestamp type
Change type in setters
SERVER-7172 Add SafeNum support to mutablebson
Remove BSONElement compatability API's from mutable BSON
Update append methods in mutable BSON to return Status
Rename Context to Document
Fix Element::getOIDValue to return a correct OID
Add a root Element to each Document
Tighten up resource management in Document
Remove appendElement which misleadingly ignores the field name
Inline Element lifecycle methods
Modernize and normalize mutable BSON headers
Don't use StringData to transfer OIDs in mutable BSON
Cast to long long to avoid ambiguity in append call