Mathomatic 15.6.3

Source code and user documentation cleanup and corrections.

Creating a PDF book from the Mathomatic man pages with "make bookman" is more
likely to work now. Package txt2man must be installed to run "make bookman".

6/24/11 - Added file misc/known_bugs.txt, which is the current list of known
          bugs in Mathomatic.

7/04/11 - Added file tests/quadratic.in, just a script that solves the general
          quadratic equation.

7/06/11 - Fixed error messaging to not always give command usage information
          when a command fails or gives a negative result.
          Now only gives command usage info when helpful,
          like when something on the command line is incorrect.

7/07/11 - Fixed the Mathomatic derivative command to not fail with a helpful
          error message when the derivative is zero.
          Now it just gives a warning message along with the successful
          result of the constant zero.

7/23/11 - Mathomatic no longer compiles correctly with the latest Xcode gcc,
          due to a bug in Apple's gcc optimizer. Either turn the optimizer
          completely off when compiling with Xcode, or use the gcc provided
          by MacPorts. Xcode version 3.x and other non-Apple C compilers will
          work fine. All mention of Xcode has been removed from the
          Mathomatic distribution.

7/28/11 - Balanced parentheses and brackets are now allowed in variable names,
          if the "set special_variable_characters" command is run first.
          For example, "set special ()" will allow entry of named functions,
          converting them to variables, which might be useful in some cases.
          However, entry of variables like "f(x)" will not be differentiatable,
          because there is no "x" variable in that, only the "f(x)" variable.
          There can be no spaces encountered in the function; variable names
          end at any non-variable character, including space characters.

          Entry of array elements is still possible with "set special []".
          This is the default.

7/29/11 - Prompts are now blue when reading files into Mathomatic in color mode.

7/30/11 - Allow an equation number range on the solve command line, for faster,
          more automated solving. If you want to solve all entered equations
          for x, just type "solve all x" or "solve verify all for x" to be sure.

7/31/11 - Allow "repeat read filename" command, which repeatedly reads a script
          until it fails or is aborted.

8/04/11 - "make install" now shows if installed executables are new or have
          changed since the last install.