We cannot trust 'mkdir -p' to set the proper permissions on parent
directories. So create them manually.
Fix handling of paths containing spaces.
Properly prefix the path with './' if it starts with a '-'.
Stop trying to create a path after the first error.

Also use the whole device surface if one of the extents is zero or 
negative and the mapping mode is MM_ANISOTROPIC or MM_ISOTROPIC.
New tests.

We are only checking against GL_MAX_TEXTURES when binding samplers,
when we should be checking against the maximum number of samplers that
the card supports.  Spotted by H. Verbeet.