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>
Minor nit: (I know it's not in this patch) I'd use .bz2 instead of .gz.  That's how all the cool kids are doing RPMs these days.