[chromedriver] Release 0.5

[chromedriver] Release 0.5

Release version 0.5 as Beta. Main changes from last release are as below:
1. Fixed issues on navigation and frame javascript execution context.
2. Added optional 'promptText' parameter to DevTools Page.handleJavaScriptDialog.
3. Added command implicitlyWait. 
4. Made session commands run in separate session threads.

NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=190486

[chrisgao (Use stgao instead), 2013-03-25 20:41:32]

ptal

[kkania, 2013-03-25 20:49:52]

add brief description about what has changed, and modify run_buildbot_steps.py
to drop the alpha

lgtm

[commit-bot: I haz the power, 2013-03-25 21:37:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/chrisgao@chromium.org/12703023/2002

[commit-bot: I haz the power, 2013-03-25 21:41:26]

Change committed as 190486