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
Skip guvectorize object error
added complex functions to npymath
fix previous merge
Test hypothesis that the problem is caused by missing GIL.
Typo fix
small refactor in scalar tests.
Initial return value to zero
added check for PyError_Occurred to fix issue #539
Clean up
Refactor