Attempt to add back support for builddir != srcdir. Use absolute paths
instead of relative paths based on pcfiledir this time to make things
clearer - there's not really any need for uninstalled trees to be
relocatable without re-running configure.
I don't know how this ever worked, as it seems to put -I./..
and -I./../libs verbatim into the includes, at least with
current autotools versions.
This reverts commit 279a80ff27.
When you use gstreamer uninstalled and build outside
the source tree, the includes need to be specified for
both the source tree and the build tree.
Signed-off-by: David Schleef <ds@schleef.org>
