Remove $Id$ tags, update URL's, and more

- remove obsolete svn '$Id$' tags from all source files
- update .fl files and generated files accordingly
- replace 'http://www.fltk.org' URL's with 'https://...'
- replace bug report URL 'str.php' with 'bugs.php'
- remove trailing whitespace
- fix other whitespace errors flagged by Git
- add and/or fix missing or wrong standard headers
- convert tabs to spaces in all source files

The only relevant code changes are in the fluid/ folder where
some .fl files and other source files were used to generate
the '$Id' headers and footers.

jpeg/Makefile

@@ -2,8 +2,6 @@
 #  FLTK - DO NOT CHANGE when upgrading the JPEG library, unless required. *
 # *************************************************************************
 #
-# "$Id$"
-#
 # JPEG library makefile for the Fast Light Toolkit (FLTK).
 #
 # Copyright 1997-2011 by Bill Spitzak and others.
@@ -12,11 +10,11 @@
 # the file "COPYING" which should have been included with this file.  If this
 # file is missing or damaged, see the license at:
 #
-#     http://www.fltk.org/COPYING.php
+#     https://www.fltk.org/COPYING.php
 #
-# Please report all bugs and problems on the following page:
+# Please see the following page on how to report bugs and issues:
 #
-#     http://www.fltk.org/str.php
+#     https://www.fltk.org/bugs.php
 #
 
 include ../makeinclude
@@ -145,7 +143,3 @@ depend:	$(OBJS:.o=.c)
 include makedepend
 
 $(OBJS):	../makeinclude
-
-#
-# End of "$Id$".
-#