Commented code removed, and assertion added to check that call to sys.getrefcount does nots changes the refcount.

Update test function test_pycuda_memory_to_theano() to fix Python 3 error.

The refcount of a variable seems to be different between Python 2 and Python 3. So it seems better to stock an initial refcount in a variable and then do the checkings with that variable instead of directly using comparing to constant values.

Tests passed with Python 3 (Anaconda):

```
$ nosetests --verbose --nocapture theano/misc/tests/test_pycuda_theano_simple.py
Run pycuda only example to test that pycuda works. ... ok
Simple example with pycuda function and Theano CudaNdarray object. ... ok
theano.misc.tests.test_pycuda_theano_simple.test_pycuda_memory_to_theano ... 4
gpuarray ref count before creating a CudaNdarray 4
strides (20, 5, 1)
gpuarray ref count after creating a CudaNdarray 5
gpuarray ref count after deleting the CudaNdarray 4
ok

----------------------------------------------------------------------
Ran 3 tests in 0.297s

OK
```

#2801:subtensor-incsubtensor

Import numpy

[REG, CRASH] fix crash related to float16 introduced in gh-5077

warn when profiling.ignore_first_call isn't used.

Make test for cast to/from int/float16 and make sure to have a cast in the inner graph instead of identify. (it was still working with identity, but having an explicit cast is better)

Fix cache

Fix crash introduced by gh-5077 by keeping GpuElemwise as original and only casting to float16 in the code generator.

Add a method to properly convert the graph of Composite to float32.

Gpuarray pool grad grad