The intention is to improve (and minimize) diffs when dependencies
are changed and `make depend' is executed.
(1) use `makedepend ... -w 20'
(2) `sort -u' the resultant file with some more "magic".
(1) makes sure that there is only one dependent file per line,
(2) makes lines unique since `makedepend' can output one file
many times which is redundant and makes diffs hard to read.
This uses 'mv', 'grep', and 'sort' in all FLTK library Makefiles.
Image libraries are intentionally left for a later update.
80ad88555f