Add fieldsplit solving test for mixed Poisson (no bcs)
Add fieldsplit test for mixed Poisson with bcs
Stash compiled kernels on the form to save recompiling
Fix docstring of clear_cache
Return early if not rank 0 when ensuring cache dir
Broadcast md5 of firedrake_geometry.h from rank zero

Again, no need to touch the disk on every process.
Silence ffc output except on rank zero
Merge pull request #240 from firedrakeproject/mixed-poisson-fieldsplit

Add more tests of fieldsplit solves for mixed poisson.
Lint fix
Merge pull request #248 from firedrakeproject/stash-kernels-on-form

Save the compiled kernels in the form_data for later reuse.
Merge pull request #249 from firedrakeproject/origin/fix/disk_cache

Remove incidences of all processes writing or reading from disk cache.
Added interior facet + mixed/vector fs test