Dr.Memory on Windows complains bitterly about invalid heap free as
it doesn't seem to be able to track this function's allocations. As
it's such a trivial function we can just implement it locally.
We previously used strstr, which can be prone to false positives when
the name of one extension is a substring of another extension.
This commit creates the helper function util_hasGLExt, which asserts
that the substring found in extension list is bounded by either spaces
or the beginning/end of the string.
