Define the rest of the khrplatform.h types, and prevent its inclusion.

One of the problems with krhplatform.h (besides it being a terrible
idea in the first place) is that it's not present on many systems at
all, including apple, win32, and linux before late 2009.

So, unless we introduce the first ./configure dependency to the core
library build, we really do need to define these standard types to
their standard values.  But if we allow khrplatform.h inclusion as
well, we'll get long-vs-int redefinition warnings on 32-bit.  So, we
have to completely replicate the header, which is a thing we've done
for everything else except for eglplatform.h.

A testcase will be used to make sure that our types don't drift from
the system khrplatform.h types, if it even exists.

Fixes #17
Add a test that khrplatform.h (if present) agrees with us.
Use the same typedefs as upstream khrplatform.h in a couple cases.

This should avoid any differences we might end up with compared to
system khrplatform.h.
Add a missing \n on an error message.