ext/ladspa/gstladspa.*: Halfway-ported. Doesn't compile yet.

ext/ladspa/gstladspa.*: Halfway-ported. Doesn't compile yet.

Original commit message from CVS:
2005-08-25  Andy Wingo  <wingo@pobox.com>

* ext/ladspa/gstladspa.h:
* ext/ladspa/gstladspa.c: Halfway-ported. Doesn't compile yet.

* ext/ladspa/gstsignalprocessor.h:
* ext/ladspa/gstsignalprocessor.c: New files, the start of a base
class for DSP elements.

* configure.ac: Sort the external libs checks, add a ladspa check,
output the ladspa makefile.