Bug 20581: Unit tests for status_alias

Bug 20581: Unit tests for status_alias

This patch adds unit tests for the specific status_alias functionality
added in this bug

- Creation of the ILLSTATUS authorised value
- Illrequest->statusalias accessor
- Illrequest->status overloading to reset status_alias

To test:
1) Apply this patch
2) prove t/db_dependent/Illrequests.t

Signed-off-by: Niamh.Walker-Headon@it-tallaght.ie
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>