Bug 15533: Fix 'ambiguous' SQL query in CanItemBeReserved

Bug 15533: Fix 'ambiguous' SQL query in CanItemBeReserved

Adding reserves.itemtype made a query to fail in CanItemBeReserved.
This patch prefixes the column names with the corresponding table names
to prevent that.

You can trigger the error by running
  prove t/db_dependent/Holds.t

You should see something like this:
  Column 'itemtype' in where clause is ambiguous

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>