Removed VMatrix SF.CheckType for self metamethods.

Fixes #36
Fixed VMatrix __mul metamethod. Now uses lhs*rhs.

Check #36
Merge pull request #72 from awilliamson/I36

VMatrix SF.CheckType Fix & __mul metamethod fix.
Change ents library registration to register under "entities"

Fixes #59
Renamed ents.lua to entities.lua in libs_sh, libs_sv, libs_cl.

See #59
Merge pull request #73 from awilliamson/I59

Rename ents to entities for Library & files.