Add a tabKey to the LoadModule message so that we can differentiate between
a reload in the same tab and opening a new tab, if the plugin has that
capability.

Also, rename write* methods for better symmetry and more tests/doc.

Patch by: jat
Review by: amitmanjhi


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@5936 8db76d5a-ed1c-0410-87a9-c151d255dfc7