make adjustments when removing layers provided by specialized pads
- gui_inst.c: moved gc construction from gui_draw_pad and gui_draw_rpad to
shared pad_gc
- layer.h: new home of all definitions related to pads and layers
- layer.c:
- overlap.c: functions to test for overlaps of pad shapes (in progress)
git-svn-id: http://svn.openmoko.org/trunk/eda/fped@5634 99fdad57-331a-0410-800a-d7fa5415bdb3
