add .spec for rpm build, minor packaging fixes

- use pkginclude_HEADERS so that make install puts the header in
  /usr/include/cgmanager/cgmanger-client.h instead of directly in
  /usr/include. We'll need to fix the path used in lxc.

- put libcgmanager.pc in $(libdir) see here for why:
  https://lists.linuxcontainers.org/pipermail/lxc-devel/2012-September/002643.html

- fix make -j by adding cgmanager and cgproxy as deps for building
  their manpage since help2man runs them to generate it

- add libnih and libnih-dbus to .pc as requires so
  pkg-config --libs libcgmanger outputs them

Signed-off-by: Dwight Engen <dwight.engen@oracle.com>
Signed-off-by: Serge Hallyn <serge.hallyn@ubuntu.com>