Merge pull request #36 in ZP/z-push from feature/ZP-678-allow-to-autoload-backends to develop

* commit '86eea041':
  ZP-678 Allow to autoload backends. Released under the Affero GNU General Public License (AGPL) version 3. Do not try to include backend, if it can be or is already autoloaded. Allows to place backends outside z-push package.

src/lib/core/zpush.php

@@ -485,7 +485,7 @@ class ZPush {
                 $loaded = false;
                 foreach (self::$autoloadBackendPreference as $autoloadBackend) {
                     ZLog::Write(LOGLEVEL_DEBUG, sprintf("ZPush::GetBackend(): trying autoload backend '%s'", $autoloadBackend));
-                    $loaded = self::IncludeBackend($autoloadBackend);
+                    $loaded = class_exists($autoloadBackend) || self::IncludeBackend($autoloadBackend);
                     if ($loaded) {
                         $ourBackend = $autoloadBackend;
                         break;
@@ -494,7 +494,7 @@ class ZPush {
                 if (!$ourBackend || !$loaded)
                     throw new FatalMisconfigurationException("No Backend provider can not be loaded. Check your installation and configuration!");
             }
-            else
+            elseif (!class_exists($ourBackend))
                 self::IncludeBackend($ourBackend);
 
             if (class_exists($ourBackend))