Update configure.in for automake 1.13.x

The new automake 1.13.x complains that AM_CONFIG_HEADER is an obsolete macro and refuses to finish during the autogen.sh step. I needed this patch to get jzmq to build jzmq successfully on Mac OS X 10.8.2 with automake 1.13 installed via homebrew.
Merge pull request #144 from benjaminfjones/patch-1

Update configure.in for automake 1.13.x