Merge "Document return of void in Maintenance::execute"

diff --combined maintenance/Maintenance.php
index 0015bbe,7e5aa31..866f959
--- 1/maintenance/Maintenance.php
--- 2/maintenance/Maintenance.php
+++ b/maintenance/Maintenance.php
@@@ -203,7 -203,7 +203,7 @@@ abstract class Maintenance 
        /**
         * Do the actual work. All child classes will need to implement this
         *
-        * @return bool|null True for success, false for failure. Not returning
+        * @return bool|null|void True for success, false for failure. Not returning
         *   a value, or returning null, is also interpreted as success. Returning
         *   false for failure will cause doMaintenance.php to exit the process
         *   with a non-zero exit status.
@@@ -1606,9 -1606,6 +1606,9 @@@
                if ( wfIsWindows() ) {
                        return $default;
                }
 +              if ( Shell::isDisabled() ) {
 +                      return $default;
 +              }
                // It's possible to get the screen size with VT-100 terminal escapes,
                // but reading the responses is not possible without setting raw mode
                // (unless you want to require the user to press enter), and that