Unit tests for the CALS package. Usage:

$ export TEXINPUTS=`pwd`/../dev:
$ mkdir tmp
$ python support/run_tests.py
  or, to execute a subset of the tests,
$ python support/run_tests.py cell/test_10

Expect that the tests in the directory "visual_tables" fail.
Depending on the OS and TeX distro version, the font drawing
might look different.
17 Nov 2014: the tests in "visual_tables" are disabled.

Probably I need to package the unit testing code as a separate
package and publish an article about it.
