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>