Clean up spec file.

Include missing psm_am.h header in dist tarball.
Don't define %{buildroot}: this is only needed on RPM <= 4.6.
Fix other minor rpmlint errors (currently at 0 on RHEL7, RHEL6.4).

Allow --with options to be specified on rpmbuild command line like:

rpmbuild --with valgrind -ba ...  # build with valgrind
rpmbuild --without dlopen -ba ... # build without dlopen -ldl

Allow RPM installation under specified prefix (works like DESTDIR):

rpm --prefix=$HOME/local -ivh ...

Signed-off-by: pmmccorm <patrick.m.mccormick@intel.com>
Actually, I think you need to put a real date in there.  rpmbuild refuses to run when I have "XX" in there:

```shell
$ rpmbuild --without dlopen -ba libfabric.spec |& tee rpmbuild.out
error: bad date in %changelog: Wed Jan XX 2015 Maintainer Name <email@intel.com> 1.0.0
```