This uses the virtual /proc filesystem to identify when the user runs
`python` without redirecting stdout/stdin. If this is the case, we run
`python -i` instead. Otherwise, or if there are arguments, we run it
verbatim.

R=dnj@chromium.org
BUG=598956

Review URL: https://codereview.chromium.org/1851113003 .

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@299681 0039d316-1c4b-4281-b951-d872f2087c98