Correct a bug in xsil2graphics2 for MATLAB/Octave export of ASCII data files.

git-svn-id: svn+ssh://svn.code.sf.net/p/xmds/code/trunk/xpdeint@2908 41b19578-b77a-4e3b-9682-c8570d237623
Various minor improvements to the Modified-Midpoint stepper and the Richardson Fixed Step integrator.

git-svn-id: svn+ssh://svn.code.sf.net/p/xmds/code/trunk/xpdeint@2909 41b19578-b77a-4e3b-9682-c8570d237623