New search UI tweaks:

New search UI tweaks:
* Show namespace checkboxes only for advanced search. Showing these for "Project Pages" searches
does provide information for advanced users, but clutters UI for everyone else. User should be able to
refer to help pages to find out which namespace are in "Project Pages" and these are also in tooltip
* put "did you mean.." inside the fieldset for increased visibility
* missing 'advanced' req param was making advanced form behave strangely, fixed
* remove "browse pages with this prefix", clutters, sometimes shows up, sometimes not. User cannot tell why
if not familiar with namespaces and logic behind the it (e.g. it shows only when one namespace is selected)
* correct placement of external search box when search is disabled
* make search messages consistent for new and existing pages