Use x-friends instead of x-internal to expose jgit for internal use

This prevents a lot of unnecessary warnings about disouraged usage of
the org.eclipse.jgit.internal package within JGit itself.

Change-Id: Ia6683902809425fd7245e7d5d344c2ff8f317ebb

org.eclipse.jgit/META-INF/MANIFEST.MF

@@ -14,7 +14,7 @@ Export-Package: org.eclipse.jgit.api;version="2.2.0",
  org.eclipse.jgit.events;version="2.2.0",
  org.eclipse.jgit.fnmatch;version="2.2.0",
  org.eclipse.jgit.ignore;version="2.2.0",
- org.eclipse.jgit.internal;version="2.2.0";x-internal:=true,
+ org.eclipse.jgit.internal;version="2.2.0";x-friends:="org.eclipse.jgit.test,org.eclipse.jgit.http.test",
  org.eclipse.jgit.lib;version="2.2.0",
  org.eclipse.jgit.merge;version="2.2.0",
  org.eclipse.jgit.nls;version="2.2.0",