Log Message:
Update mathomatic to 12.7.6.

Changes since 12.7.2:
Improved documentation.
Added display of maximum memory usage to version command.
Allow read command in the Mathomatic library and fixed memory leak with it.
Added echo command per a user's request.
Improved factoring out constants, to make all coefficients reduced integers by
  factoring out their gcd.
Added gcd_verified() function, to weed out false floating point gcds.
Made limit command say whether it is substituting or solving.
Added "mathomatic.desktop" and "mathomatic.png", which are \ 
the desktop and
  icon files for Linux.
Minor code, documentation, and makefile improvements.
Added "tests/quartic.in" and fixed incomplete simplification in the \ 
calculate
  command.
Allow upper case when parsing infinity constant name "inf", required \ 
by CygWin
  version and maybe others.
The makefiles no longer strip the created executables.
Reordered source code so many functions can be defined returning \ 
"void" (which
  means no return value).
Added "tests/how_limit_works.in" tutorial and restored \ 
"doc/notes.html".
Testing change to only one kind of partial unfactoring (partial_flag =
  true/false, default true), completely distinct from full unfactoring. Used
  throughout, let me know if this breaks anything.
Added "simplify fraction" option, which simplifies like Maxima's ratsimp().