Factor out writing of common compiler settings and setting of common defines.

Factor out the writing of HAVE_* defines in include/config.h and sort
the resulting defines before writing.

msvcmaker: Fix the generated filename for the spec file for modules with extensions other than .dll.

This gets make_opengl to work again with Perl 5.10.

This prevents the target from changing during the first PreLoad() call
on a surface, which would be inconvenient when attaching a surface to
a FBO for example.

This creates a function for setting the texture name and one for
setting the texture target. The idea is that the texture target should
get set right after the surface is created, and won't change, while
generating a texture name can wait.