Remove superfluous leading './'s

When running a script in another directory via a relative
path it's not necessary to have a leading ./ regardless of
your PATH.  (At least that's is the case with bash, zsh,
tcsh, csh and dash.)
Create a xapian database on Travis to fix a test failure

The error in this case was:

     1) RequestController when showing similar requests should work

    Failure/Error: get :similar, :url_title => info_requests(:badger_request).url_title

    RuntimeError:

    Failed to open Xapian database /home/travis/build/mysociety/alaveteli/vendor/plugins/acts_as_xapian/lib/../xapiandbs/test: DatabaseOpeningError: Couldn't stat '/home/travis/build/mysociety/alaveteli/vendor/plugins/acts_as_xapian/lib/../xapiandbs/test'

This seems to be fixed by adding script/update-xapian-index
to the setup on Travis.