fix for 0006297: sorting on custom field, bring MySQL to deadlock loop

• thanks to MTW
  fix for 0006296: Filter sql includes unnecessary links to custom_field_string_table for date custom fields
  fix for 0006295: Old filters and view_state problems.
  fix for 0006288: Patch against CVS HEAD for Saved filter problem with view_state

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@3858 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9