Make upgrades log full sql errors

The upgrade error logs have truncated details of sql error :

example:
error for upgrade to alpha 1
DB Error: unknown error
#0 [internal function]: CRM_Core_Error::exceptionHandler(Object(DB_Error))
#1 /..site/administrator/components/com_civicrm/civicrm/packages/PEAR.php(931): call_user_func(Array, Object(DB_Error))
#2 /..site/administrator/components/com_civicrm/civicrm/packages/DB.php(968): PEAR_Error->PEAR_Error('DB Error: unkno...', -1, 16, Array, 'ALTER TABLE civ...')
#3 /..site/administrator/components/com_civicrm/civicrm/packages/PEAR.php(564): DB_Error->DB_Error(-1, 16, Array, 'ALTER TABLE civ...')
#4 /..site/administrator/components/com_civicrm/civicrm/packages/DB/common.php(1903): PEAR->raiseError(NULL, -1, NULL, NULL, 'ALTER TABLE

http://forum.civicrm.org/index.php/topic,25790.msg109049.html#msg109049

And makes it difficult to detect the sql errors without looking at database.

As discussed with tim - This may mean refactoring CRM_Core_Error::backtrace to provide consistent formatting for bot types of backtraces.