Throw error on empty domains in min/max

See merge request !104

Add global barrier helper functions to loopy

See merge request !101

Nosync updates

Closes #60 and #51

See merge request !102

* Make *add_nosync* visible in the loopy docs.

type. Now, the argument to a reduction can be either a scalar or a
tuple.

This reverts commit 7913e68a.

Conflicts:
	loopy/transform/iname.py
	test/test_loopy.py

either a tuple, reduction, or a substitution invocation).

Also, rewrite the reduction mapping code to rely on recursive calls
map_tuple(). This cleans up a lot of reduction mapping code
substantially.

# Conflicts:
#   loopy/transform/iname.py

* Eliminates inames arguments to reduction functions (closes #32).
* Changes the argmax function to accept two arguments.

See also: #62

This reverts commit b0232906.

This reverts commit 967414c7.

recursive_insn_dep_map().

# Conflicts:
#   test/test_loopy.py