Add some functions to allow certain pages to run longer than the default timeout of 30 seconds.

• config_defaults_inc.php
  (long_process_timeout): new config option to set how many seconds are given
  long-running pages like database upgrades

• admin/upgrade_inc.php
  (UpgradeSet::run): display a warning that the process may take a while and
  register the process as long-running. Also disable compression and flush
  the output buffers in an attempt to enable streaming.

• core/helper_api.php
  (helper_being_long_process): new function to set up PHP to allow a page to
  run for an extended period of time. Currently used in database upgrades
  but might be useful in project deletion and view_all if we can't speed
  them up ugh

git-svn-id: http://mantisbt.svn.sourceforge.net/svnroot/mantisbt/trunk@1939 <a class="text" href="/?p=mantisbt.git;a=object;h=f5dc347c">f5dc347c</a>-c33d-0410-90a0-b07cc1902cb9