Special:Export, when doing 'add pages from namespace',
passes the form parameter "nsindex" back to the server.
This "nsindex" is primarily used to pick pages, but should be used to
set that <option selected> when the form is returned to the user.
Unfortunately this information is thrown away, and the selector flies
back up to the default (first, NS_MAIN) value. The user has to figure
out where he was and what he was doing all over again.
This patch fixes it.
Note, the form still lacks a reset button.
If one wants to start over clean, and is not a power user.