More GCC bug workarounds

4.6 now produces bad code for some kernels unless we turn tree-vectorize
off.
Move back to PETSc/petsc4py master
Add versioneer 0.10
Hook up versioneer in setup.py
Install versioneer

This file helps to compute a version number in source trees obtained
from git-archive tarball (such as those provided by githubs
download-from-tag feature). Distribution tarballs (build by setup.py
sdist) and build directories (produced by setup.py build) will contain
a much shorter file that just contains the computed version number.

The PyOP2 package version now includes the git revision as returned by
  git describe --tags --dirty --always
Set versioneer default to string set in version.py
Default COFFEE configuration to GNU compiler / SSE ISA
Add context manager for timing a given code region
Profiling: add a Timer.reset method
Profiling: add timing method to get average time for task
Rename profile decorator to timed_function
Add timed region around sparsity building
Add timed region around PETSc KSP solve
Time ParLoop compute, halo exchange, reduction
Add configuration option to print summary at exit

Either set the print_summary configuration option or export
PYOP2_PRINT_SUMMARY
Profiling: get_timers can optionally reset all timers