Change Repository.getConfig() to return non-file Configs

A repository implementation might support storing configurations
on a non-file storage system, so widen the return value to be any
type of configuration.

Change-Id: If9a0928f4b3ef29a24d270b0ce585a6e77f6fac6
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit/src/org/eclipse/jgit/lib/Repository.java

@@ -154,7 +154,7 @@ public abstract class Repository {
 	/**
 	 * @return the configuration of this repository
 	 */
-	public abstract FileBasedConfig getConfig();
+	public abstract Config getConfig();
 
 	/**
 	 * @return the used file system abstraction