Don't distribute version.rb

version.rb is built from version.rb.in by `make`, so it shouldn't be distributed, but it should be installed.

Should fix #133. Assuming it does, I'll release this as v1.5.1.

@mike-burns, @pbrisbin, @cippaciong: Could one of your build a tarball from this branch (`make distclean && ./autogen.sh && ./configure && make distcheck`) and the try installing from that tarball?