Fixed incorrect parsing of Number type.
Fixed cases of int.Parse() and float.Parse() to use the invariant culture.
Added a comment to clarify things.
Merge pull request #2724 from SickheadGames/mgfxculture

MGFX Fixes
Fixed possible ArgumentNullException in ContentTypeReaderManager.

ContentTypeReader.TargetType can be null, e.g. for ExternalReferenceReader.
Merge pull request #2725 from DigitalRune/contentreader

Fixed possible ArgumentNullException in ContentTypeReaderManager.