Added VELCOIraptor linker flags to Makefile.am instead of adding it directly to the LIBS environment variable.

Currently ParMETIS is used exclusively when it is available, it is not an error to configure with both METIS and ParMETIS

When not explicitly given checks for GSL are made anyway, when explicitly given the checks must be successful

Add a separate timer for subset sub-cell tasks. Write the timers to a file. Make sure we can compile without timers. Add a configure option to switch the timers on.

Tidy up so that both trees use the same library dependencies