- change_world.c: fixed critical bug where ID[5] was being set to
  patchID instead of vegid for calls to find_tlevel, which caused all
  patches to not be found.

- makefile: set -g as default instead of -O to make debugging possible

- main.c: Added 'mask' command line option.  If not supplied, will try
  to use a raster mask named 'mask'

- main.c: enforced proper use of EXIT_FAILURE and EXIT_SUCCESS

- blender.h: changed MAXS from 80 to 1024 to allow lairead to be
  called using absolute paths