BUG: Fix a typo

This commit fixes the following error:

 PHP Notice:  Undefined variable: coveragestatus in
 /var/www/cdash/ajax/getviewcoverage.php on line 299
ENH: Support PostgreSQL in filter data functions

Tested-by: Nils Gladitz <nilsgladitz@gmail.com>
BUG: Fix undefined variable usage in test viewer.

This commit fixes the following issue:

  PHP Notice:  Undefined variable: extras in /var/www/cdash/viewTest.php on line 273,
  referer: http://localhost/cdash/viewTest.php?buildid=391
ENH: Check that git directory is writeable

and avoid undefined index usage if it's not.
BUG: Fix a minor PostgreSQL incompatibility in test failure graph viewer

This patch fixes the following error:

  PHP Notice:  Undefined index: count(*) in /var/www/cdash/ajax/showtestfailuregraph.php
  on line 74
BUG: Fix undefined variable usage in changes viewer

This commit fixes the following error:

  PHP Notice:  Undefined index: checkindate in /var/www/cdash/viewChanges.php
   on line 355
ENH: Drop remnants of backup page that was removed in r2599
BUG: Display correct configure warnings number on build summary page.
BUG: Overhaul configure warning extraction algorithm

This fixes warnings duplication and makes extraction actually work.
The algorithm can be further improved.