Add result checking to jac apps.

The jac apps return 0 when the solution is correct and 1 otherwise.
The testing is robust to changes in grid size but not to the number
of iterations.
Need to gather data for all ranks before doing results check
Add results check to jac 2 test case
Use the correct stride for jac2 results checking
Add rudimentary regression test Makefile
Simplify results check
Merge pull request #56 from OP2/jac-testing

Jac testing

Adds a simple regression test to the Jacobian demos. Returns 0 if passed or 1
if failed. Also adds a rudimentary regression test. Run `make test` in the
'apps/c/bin' folder. MPI tests will be run with `mpirun -np 4`. Override by
either adding `NPROCS=N` to run with a different number of processes or
`MPIEXEC=mpiexec` to use an entirely different command to run the MPI job.