This patch adds a language environment for the Catalan language.

It is needed in order to get word motion commands work correctly, as in
Catalan the middle dot character `·' is a word constituent.  This is done by
changing the syntax class of the middle dot character.

Changes made:

        * international/mule-cmds.el (locale-language-names): Map locale
          language name `ca' to language environment `Catalan'.

        * language/european.el: Add definition of language environment for
          the Catalan language.

        * leim/quail/latin-pre.el: Add quail rule to the `catalan-prefix'
          input method to support input of middle dot characters through
          composition.
        
This is a trivial patch based on a post by Dave Love on the help-gnu-emacs
mailing list [1], and therefore I believe a copyright assignment from me is
unnecessary.

[1] http://lists.gnu.org/archive/html/help-gnu-emacs/2009-11/msg00008.html