Allow user-defined keys in config files.  Use SafeConfigParser.
Allow user-defined keys in config files.  Use SafeConfigParser.

This allows us to use interpolation in the config files, which is handy
for setting the certain flags which should be the same for both
optimised and debug builds.

ruthfranklin/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande,hande-qmc/hande