overhaul shadowing
add get_value for sharedvars
allow simple_call default with no args
top_node -> top_def
add check for np.number
test signatures
rename ad -> sym
move clean_int_args to utils
sym_outputs are now passed directly
expand call
clean up; tag is handled by context now
add back comparisons to ensure compatibility with NumPy < 1.8
handle globals, varargs, kwargs and defaults properly during recompilation
minor updates