Modified download_toolchains.py to allow specifying a toolchain root directory
Modified download_toolchains.py to allow specifying a toolchain root directory

This is needed by the SDK so that the SDK can download the toolchain
in the SDK's toolchain directory instead of NaCl's toolchain directory.

Also, fixed pychecker warning about 'hash'


BUG=None
TEST=Trybots


Review URL: http://codereview.chromium.org/7712016

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@6511 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client,nacl-webkit/native_client