CRM-16587 - workaround selected records custom search.

CRM-16587 - workaround selected records custom search.

This is a workaround, and it will probably not work 100% in these cases:
* if you need to select columns with identical names from different tables
* if you need expressions in your SELECT statement, instead of just selecting
  a column.

You also have to adapt your custom searches for this to work. I changed
the PostalMailing custom search so that you now can apply actions on a
selection of the retuned records.

----------------------------------------
* CRM-16587: Action menu is not available on selected records on a Custom search
  https://issues.civicrm.org/jira/browse/CRM-16587