Format commit logs

Format of commits

See http://www.nmr-relax.com/manual/Format_commit_logs.html

Example 1

Fix for bug #20915, (https://gna.org/bugs/?20915) - Failure of Grace opening
in MS Windows

My name provided this patch, and was discovered during work on a
Windows 7 system: name _aaattt_ domain_dot_com

This is a small fix for a wrong call to "raise
RelaxMissingBinaryError(binary)", when issuing an external call to xmgrace.

The "path_sep" would be equal = [/], and the RE search would not find(True)
the full path specified for the xmgrace file.
This is now shifted to python: os.path.isfile
http://docs.python.org/2/library/os.path.html

Another fix, is that as a standard the command "xmgrace" is provided. This
will work fine through windows cmd, but the true name for program in windows
is "xmgrace.exe", and so an additional search for +".exe" is also performed.