Fix brace indents, various code cosmetics/comments.
No functionality changed yet; preparation for STR #2991 mods.



git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10002 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
STR #2991: No functionality changed.
	   Simplify used_colors[]: replace uchar array with rgb struct.



git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10003 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Fixes STR#2991: prevents crash when file browser
                encounters an image that can't be loaded.



git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10004 ea41ed52-d2ee-0310-a9c1-e6b18d33e121