sometimes pd is run in non-gui environments (e.g. with
it is desireable that one can build such a gui-less pd,
without having to install the tcl/tk-headers.
the patch adds a "--disable-tk" flag to configure and
only sets the GSRC in makefile.in if tk is enabled.
this has been in the feature request tracker.
the patch only modifies configure.in and makefile.in;
in order to work, one must run "autoconf" to generate a
proper configure file.