dx9: Fix splines and beziers in Direct3D.

Fixes #7181.
dx9: Clean up some differences in spline code.

Hmm, the spell effects look wrong.  Maybe a separate bug.
GLES: Merge the two ShaderID classes as they are identical.

I don't expect the number of bits required to grow or shrink massively for either type of shader in this backend.
Add a sanity check for shader linking, active in debug mode
GLES: Implement a custom modulo function for PowerVR. Fixes blockiness, see #7153 and #7150
Reduce PowerVR blockiness problems on older GPU revisions. #7153 #7150
Try having travis notify us on build failure.
Remove some unused functions.
Fix some type comparison warnings.
Update native (buildfix.)