Relax nopython restriction for gufunc
Add test for gufunc object mode
Test object modes and forceobj in ufunc builders
Add error handling for gufunc object mode
Fix invalid decref
Clean up
- make call wrapper initializes the return value to zero so that null must be returned when an error occurs in object mode function
Add docstrings
Merge branch 'master' into gufunc_object

Conflicts:
	numba/cgutils.py
	numba/npyufunc/wrappers.py
	numba/targets/cpu.py
Add environment object to gufunc builder
Fix env keepalive
Fix CUDA CC support.
- Auto fallback to highest compute capability
- Add env variables to force CC
Skip guvectorize object error
Test hypothesis that the problem is caused by missing GIL.
Typo fix
Merge pull request #641 from sklam/cuda_cc50

Fix CUDA CC support.
Initial return value to zero
Clean up
Refactor
added llvm version check
added test for llvm version check