Fix xcompositeCreateRegionFromBorderClip return type

The XCompositeCreateRegionFromBorderClip() function returns an Xfixes
region (an XID), not an Xlib region, so a wrapper function and
makeRegion invocation are unnecessary.

The FFI definition for this function returns a plain XID instead of
a Region to avoid adding Xfixes as a package dependency.
Merge pull request #1 from anthonyde/fix-region

Fix xcompositeCreateRegionFromBorderClip return type