doc/library/tensor/basic.txt: add alloc() to the list of ways of creating a tensor

Split file

Update documentation that was pointing to deprecated or removed function...

Cleanup

Fix SharedVar.value property.

reported by Drew Duncan

fix gh-1474

This was reported by @abergeron

Also move take to subtensor.py
This allow subtensor.py to depend on basic.py. This is a more sensible dependency.

This make tensor/basic.py at 191k, so lower then 200k for gh-651.

This advance ticket gh-651

Gh1461

This is needed to make the new GpuImages2Neibs ignore_border mode pass.

Also make sure the input is on the CPU, so a transfer is added when needed.

Tests