Bug 10361: (follow-up) add tests for search history functions

Bug 10361: (follow-up) add tests for search history functions

This adds tests for the new PurgeSearchHistory function and
AddSearchHistory.  GetSearchHistory is not tested due to its
current broken state (see bug 10667).

To test:

[1] Run prove -v t/db_dependent/Search_SearchHistory.t
[2] Verify that all tests pass.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>