Second attempt at landing. Fix quotes around python in "gclient.bat".

Currently, all ".bat" entry points use "~dp0python" to ensure that the
Python that is used to execute the tool is the one in depot_tools. This
prevents any sort of system override.

Remove this override so that PATH solely determines which Python is
used. To accommodate users who invoked these tools without Python on the
PATH, we still still add "depot_tools" as a catch-all PATH suffix.

Some tools were also not using DOS-style line endings. This CL fixes
this.

BUG=chromium:714293, chromium:724902
TEST=None

Change-Id: I0fceb99c8adb96e72dac706819be032d400aad37
Reviewed-on: https://chromium-review.googlesource.com/521704
Commit-Queue: Daniel Jacques <dnj@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Scott Graham <scottmg@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>