Low: Build: Allow build outside of top_srcdir
This allows the following to work:

The first hunk fixes the following error:
...
../../../lib/cib/cib_utils.c:34:33: error: lib/cib/cib_private.h: No such file or directory

The second hunk fixes the following error:
...
Making all in xml
make[1]: Entering directory
`/home/horms/projects/linux-ha/debian/experimental/pacemaker-tip/stable-1.0/tmp/xml'
cp ../../xml/pacemaker.rng pacemaker-1.0.rng
cp: cannot stat `../../xml/pacemaker.rng': No such file or directory

Signed-off-by: Simon Horman <horms@verge.net.au>

Mercurial revision: a23ff08f7523e576c12a20757d098771ee9a03aa