Run `autoreconf -vi`

I have automake 1.11.1, not 1.13.1.  And since I'll be modifying
configure.ac and Makefile.in, I want to collect all the churn into a
single place.

I'd be much happier just depnding on autoconf, and not including these
files.
Update configure.ac

Hopefully this will improve portability.  We now quote more things, ask
to check for more programs, replace a useless "test -n" with a
meaningful "test -x", use "AC_MSG_CHECKING" more, and be more compatible
with silly users who set COQBIN to ! and have a "test" that interprets
`test -n "!"` wrong, and be more compatible with crufty users who have
a "test" which barfs on 'test "" = "no"'.
autoreconf -vi
Update Makefile.am

Use $(MKDIR_P), $(LN_S), and be more uniform about $(srcdir) and
$(srccoqdir).

This closes #184.
autoreconf -vi
Merge pull request #188 from JasonGross/fixup-autoconf

Fixup autoconf. The churn is irrelevant, you will survive as an expert user. The mathematician in the street who already has a hard time compiling coq and learning git will curse you for requiring autoconf tools. And we will curse you if you bundle things in .tar.gz, thereby teaching people not to use git ;-)