ENH: riemann_compare module

New module for comparing various implementations of Riemann solvers.
added riemann shootout framework
iso_c variant
fixes #248 (riemann_compare branch)
f2py-based compile flags in Makefile
Merge remote-tracking branch 'upstream/master' into HEAD
added 2D shallow water test
Merge branch 'cudaclaw' into riemann_shootout
cudaclaw integration
don't propagate failed import
Merge branch 'riemann_shootout' into cudaclaw_shootout
whitespace fix (no semantic changes)
minor changes
removed hardcoded CELLSX and CELLSY (non-functional)
consistent non-interleaving of dofs
added interleave/non-interleave transpose, fixed sync bug
new version of params.h from gorune@gmail.com
removed typedef real (this is hardcoded by PyClaw currently to double)
cudaclaw.cu reformatting
refactored for entropy fix call, new dt_used parameter