rewrite some examples and their tests to make code more clear and optimizable
change the parakeet code generation and evaluation to avoid recompling
in each iteration
add check in distarray update to avoid computing overlap when update the
whole array
change to add op_map in the ParakeetExpr so that it won't cause error
when the expr is re-evaluated
change the test_linear_regression in test_performance
fix optimization bugs in test
write the binary search for slicing so that slicing can be faster
mv the local.py and optimize.py to next pull request
Merge branch 'master' of github.com:spartan-array/spartan

Conflicts:
	spartan/examples/cf/item_recommender.py
cancel auto optimization on expr.force due to the broadcast error on
parakeet code
Merge pull request #150 from MaggieQi/master

rewrite some examples and their tests to make code more clear and optimizable