Add missing overloaded function HashCode(const unsigned int&, const Standard_Integer&)

Fix build failure on Mac OSX 10.5, see discussion in issue #378.
Fix conflicting definitions of GLintptr on Mac OSX 10.5

See discussion in issue #378.
Merge pull request #380 from tpaviot/review/fix-build-macosx10.5

Fix build failures on Mac OSX 10.5