Merge web-mode stack trace support.

 svn merge -c 4763,4764,4804 https://google-web-toolkit.googlecode.com/svn/changes/bobv/web_mode_stack_traces_r4761

Patch by: bobv
Review by: jgw, mmastrac


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@4807 8db76d5a-ed1c-0410-87a9-c151d255dfc7