Fixes a bug where all Buttons default to submit in safari, causing forms to automatically submit when the button is pressed.  This patch introduces a button class for each button type.

Patch by: t.broyer
Review by: jlabanca
Issue: 1585, 3962



git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@6022 8db76d5a-ed1c-0410-87a9-c151d255dfc7