Allowing multiple issue servers to be autolinked in the changeset view;
linking is now contingent on issue_server_link, issue_pat and issue_prefix
being defined; multiple servers can be used by specifying a common suffix on all
the above variables, ie ..

issue_server_link_1
issue_pat_1
issue_prefix_1

.. and ..

issue_server_link_other
issue_pat_other
issue_prefix_other

.. would be treated as two distinct servers, but ..

issue_pat_thing

.. would be ignored (since the other two requisite vars aren't present).

This patch is backwards compatible with existing variables (as a suffix
isn't needed).