Atan2 function
comment back
Missing None checks in atan_2
Merge branch 'atan2' into atan2_fix

Conflicts:
	ffc/quadrature/quadraturetransformer.py
Dont import as_form from ufl.
Merge branch 'tuomas2/fix-atan2-zero-compile-error'
Merge branch 'martinal/topic-cleanup-ufl-files'
Disable | tee logfile for now in test suite since tee does not
pass on the exit status through the pipe.