Changed argmax dtype from int32 to int64

Refactored GPU install instructions

Also refactored a bit GPU tips, and removed the note about limitation to
4 GPUs (which is not true anymore).

Moved instructions from "Using the GPU" tutorial page to the intallation
instructions.

Added a link from installation instructions to the "Using the GPU"
tutorial.

Minor stuff

Fix argmax grad

Some test fixes

Fixed some tests with compute_test_value = ignore

Now also testing gradient with axis=None (failing as of this commit).

If 'axis' is empty then x.ndim must be equal to zero, and thus we also
have 'axis == range(x.ndim)'.
If x.ndim in non-zero, there is no reason for axis to be empty, so
better not catch this case.

Windows requires pickled files to be opened in binary mode.

Also rewrote file operations to be safer.

Fixed test_lazy.py and test_vm.py

Everything looks fine.

Fixed test_vm.py:TestCallbacks.test_callback_with_ifelse.

Two tests are now failing in test_vm.py

This is safer on 64 bit computers, and remains platform-independent.

fix test in FAST_COMPILE.

change the default of theano.{max,min,argmax,argmin,max_and_argmax} to t...

Changed default compiledir under Windows

Added documentation about newly-added VS files

Fix #12

This option was redundant with config.base_compiledir

A few notes:

* I went ahead and removed theano/misc/hg_version_hook.sh. It
  is not functional now, so I inferred that no one cares about
  it (file a new issue if I'm wrong!). It'll be in the history,
  should we ever want to write a git hook replacement for it.
* I made some minor whitespace fixes, including collapsing the
  unnecessary double-depth try/finally.
* I think that the _minimal_ext_cmd isn't needed, but I left it in.
* Why not do direct substitution into full_version, instead of
  writing code to do Python substitution again? Left it as is for
  now, in case there's a good reason...

This change was advocated by Sebastian Urban, who explained:
When you use roaming profiles in a domain environment the contents of
the user profile directory C:\user\xxx are transferred (copied) from a
file server at login. Login will become slow when many temporary files
are stored in this directory. Therefore they should be stored in
C:\user\xxx\appdata\local because this directory is not synchronized
with a file server. theanorc can stay where it is, because it should
roam with the user profile.

This commit actually changes `config.home` rather than
`config.base_compiledir`, because it is likely that if Theano ever wants
to save more data files (in addition to compiled C modules), the same
remark would apply.

At the same time, `config.home` is being changed to be the home
directory for Theano files, rather than the user home directory. It
was not used anywhere in Theano except to define the location of the
compilation directory, so there was no reason to keep a pointer to the
user home directory while moving the Theano compiled files to another
location.

In order for this change to be safe, an error is raised if a user
attempts to redefine `config.home` without also changing the location of
the compilation directory. Otherwise, Theano files would be compiled in
the parent of the intended folder (if the user is not aware of this
change).

Finally, note that currently, having both `config.home` and
`config.base_compiledir` is redundant, since `home` is only used to
define the default value of `base_compiledir`. So we could just decide
to get rid of `home`.

SpSum Op: pep8'ified, perform rolled back to basic (clearer/safer) implementation, and some prints remnoved from tests.