ZF-5208: Zend_Loader_PluginLoader : __constructor() breaks each
staticRegistry everytime.   Documents says that "Other
components that instantiate the PluginLoader using the same
registry name will then have access to already loaded paths and
plugins. "  But in __constructor(),each staticRegistry will be
initialized everytime.
self::$_staticPrefixToPaths[$staticRegistryName] = array();
self::$_staticLoadedPlugins[$staticRegistryName] = array();
Maybe, I supporse that these initCodes have to be checked "!
isset()".    merged back into 1.7 release branch for possible
1.7.3 release