Log Message:
Update mathomatic to 12.6.12.

Changes since 12.6.8:
12/16/06 - Add "set special_variable_character" option.
12/26/06 - Comment makefiles and add "INSTALL.txt" for first-time users.
12/31/06 - Add "primes/primorial" Python program.
2/10/07 - "make install" wasn't working - fixed.
2/24/07 - Allow calculating large powers of complex numbers at the prompt,
  like (i#+1)^99.
3/06/07 - Display which color mode is in effect on startup of Mathomatic.
3/08/07 - Some minor interface improvements to the taylor command.
3/31/07 - Corrected limit command for infinity limits.
4/3/07 - Updated root "README.txt" and created "tests/limits.in".