Allow writing to gauges when num_aux = 0.
Merge pull request #390 from ketch/gauges_without_aux

Allow writing to gauges when num_aux = 0.
added hdf5 and netcdf write/read to petsc + usage example on 2d acoustics
Merge pull request #392 from sanromd/petsc-hdf5

 hdf5 and netcdf write/read support in petsc io + example
Clean up code that creates PETSc viewers.

Incidentally, this fixes a couple of bugs/deficiencies:
- Write NetCDF instead of HDF5 when NetCDF is requested
- Allow reading of VTK
Extract common code from PETSc read and write routines into subroutines.
fixed centers and edges with ghost
Merge pull request #394 from ketch/petsc_viewer_cleanup

Clean up code that creates PETSc viewers.
Change _registers reference to copy q in SSPMS32 method.
Update expected results for tests with SSPMS32 method.
Use 2nd TVD reconstuction on 2D accoustics w/ variable coeff.
Merge pull request #401 from hadjimy/ssp_lmm_bug_fix

SSPMS32 bug fix
num_ghost fix
Add code for SSPMS43 and update computations for SSP LMM.
Update nosetests for SSPMS32.
Mostly adding comments.
Removing unnecessary variables.
Merge pull request #402 from sanromd/fix_ce_ghost

Fix calculation of ghost cell centers
Using deepcopy for stages of starting methods.
Parallel petclaw tests in Travis