webclient timeout error hangs share links tab forever

[Mike McCracken]

When attempting to share a file using the CP share links tab, it hung forever with the loading overlay.

The following traceback was in syncdaemon-exceptions.log:

2012-12-18 10:22:57,494 - ubuntuone.SyncDaemon.ActionQueue - ERROR - ChangePublicAccess share:None node:UUID('8a93e3b4-5c19-4a78-89ce-842648a08496') ChangePublicAccess(running='False') failure: ('', TimeoutError('',)) (traceback follows)
Traceback (most recent call last):
  File "ubuntuone/syncdaemon/action_queue.pyc", line 1522, in run
  File "twisted/internet/defer.pyc", line 1037, in _inlineCallbacks
  File "twisted/python/failure.pyc", line 382, in throwExceptionIntoGenerator
  File "ubuntuone/syncdaemon/action_queue.pyc", line 2267, in _change_public_access_http
  File "twisted/internet/defer.pyc", line 1037, in _inlineCallbacks
  File "twisted/python/failure.pyc", line 382, in throwExceptionIntoGenerator
  File "ubuntuone/syncdaemon/action_queue.pyc", line 930, in webcall
  File "twisted/internet/defer.pyc", line 1037, in _inlineCallbacks
  File "twisted/python/failure.pyc", line 382, in throwExceptionIntoGenerator
  File "ubuntu_sso/utils/webclient/txweb.pyc", line 165, in request
WebClientError: ('', TimeoutError('',))
2012-12-18 10:22:57,506 - twisted - ERROR - *--- Failure #17 ---
2012-12-18 10:22:57,507 - twisted - ERROR - Failure: exceptions.TypeError
2012-12-18 10:22:57,507 - twisted - ERROR - *--- End of Failure #17 ---

The last few lines of controlpanel.log are:

2012-12-18 10:22:27,453 - ubuntuone.controlpanel.backend - INFO - set_public_access_changed_handler: args (<ubuntuone.controlpanel.backend.ControlBackend object at 0x10b0511d0>, <bound method ShareLinksPanel._file_shared of <ubuntuone.controlpanel.gui.qt.share_links.ShareLinksPanel object at 0x10b66d8c0>>), kwargs {}.
2012-12-18 10:22:27,455 - ubuntuone.controlpanel.backend - INFO - set_public_access_change_error_handler: args (<ubuntuone.controlpanel.backend.ControlBackend object at 0x10b0511d0>, <function <lambda> at 0x10b6ebf50>), kwargs {}.
2012-12-18 10:22:27,460 - ubuntuone.controlpanel.backend - INFO - change_public_access: args (<ubuntuone.controlpanel.backend.ControlBackend object at 0x10b0511d0>, u'/Users/mmccrack/Ubuntu One/UbuntuOne Mac Client Builds/release-4.0/Ubuntu One.dmg.sig', True), kwargs {}.

The tab should handle errors better, showing an error message and removing the overlay so we can try again.