Merge branch 'branch-6-4' into fa-6-4

Conflicts:
	mapscript/swiginc/image.i

BUGZID:
Properly find the tclgd library.  tcl.gd needs to create a libtclgd.so symlink to the actual shared library.  It's a TEA-standard build, though.
BUGZID:
Perform the msSetup() call during Mapscript Tcl initialization to set up the font cache and threads if so configured.
BUGZID:
Merge branch 'fa-6-4' of github.com:flightaware/mapserver into fa-6-4