Rename contrib/tools/chkfmt to contrib/tools/chkfmt.sh; refactor:
* Increase the max line length for contrib/**/*.[ch] from 96 to 100.
* Set the max line length for ci_*.sh to 100.
* Use `basename $0` instead of the hard-coded script name.
* Update comments.
Remove contrib/tools/reindent. For automated code formatting, including
indentation, we need a robust solution.
Add an empty line after the hashbang line in all scripts.
Remove the "last changed" version info from comment headers.
(The version control system maintains this information automatically.)
Moved testing of bad pngs into a separate tests/pngtest-badpngs script
Added the --xfail (expected FAIL) option to pngtest.c. It writes XFAIL
in the output but PASS for the libpng test.