libgpg-error 1.15

Version 1.14 existed for just a few days before being pulled in favor of 1.15.  But the latter broke building on OS X.  I reported the bug, and [upstream made a patch](http://lists.gnupg.org/pipermail/gnupg-devel/2014-September/028748.html) which I pasted into this formula.

The patch has been committed into upstream's git repo, so it should be droppable whenever the next version comes out.