src/print_button.cxx: "Print front window" implementation (new file)
This is compiled and activated if USE_PRINT_BUTTON is defined.
The feature can be fine controlled by environment variable
'FLTK_PRINT_BUTTON' (see docs in source file).
- 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.
