Extract from the selection script templates the functions
computeScriptBase() and processMetas() and put them in
their own files.  Those files are patched into the
selection script templates by SelectionScriptLinker.
Additionally, the now-isolated files are tested
using HtmlUnit.

Thanks to amitmanjhi for helping me with HtmlUnit.

Review at http://gwt-code-reviews.appspot.com/229802


git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@7760 8db76d5a-ed1c-0410-87a9-c151d255dfc7