Fix for PR libgcj/7416:
* javax/naming/InitialContext.java (init): Use
gnu.classpath.home.url.
* java/security/Security.java: Use new properties.
(loadProviders): Accept base url; use it.
* java/lang/System.java: Document gnu.classpath.vm.shortname, and
gnu.classpath.home.url.
(gnu.classpath.home.url): Define.
(gnu.classpath.vm.shortname): Likewise.
From-SVN: r60722
