Add sort method and tensor.argsort function

Py2.4

Use other impl. of OrderedSet to prevent mem. leak

Previous implementation resulted in memory not being freed,
as exhibited in particular on theano/sandbox/cuda/tests/test_memory.py.

The version for older Python, as well as the new one, appear to work
correctly on that test.

Misc2

BUG FIX: MRG_RandomStreams shared state because of member-class initialization.

Take op [WIP]

fix Scan bug reported by abalkin

and SharedRandomStreams (and added associated unit-tests)

prevent different random number generators from sharing state.

Minor fixes (typo / doc)