Accept UTF8 BOM with BlobBasedConfig

In I1f5dc07182dbf6bba2a9f4807fdd25b475da4ead, FileBasedConfig got
support for reading a configuration with UTF8 BOM.  Apply the same
support to BlobBasedConfig, to make SubmoduleWalk able to parse
.gitmodules configurations with BOM.

Change-Id: I25b5474779952fe2c076180b96fc2869eef190a8
Signed-off-by: Doug Kelly <dougk.ff7@gmail.com>

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

@@ -79,7 +79,15 @@ public class BlobBasedConfig extends Config {
 	public BlobBasedConfig(Config base, final byte[] blob)
 			throws ConfigInvalidException {
 		super(base);
-		fromText(RawParseUtils.decode(blob));
+		final String decoded;
+		if (blob.length >= 3 && blob[0] == (byte) 0xEF
+				&& blob[1] == (byte) 0xBB && blob[2] == (byte) 0xBF) {
+			decoded = RawParseUtils.decode(RawParseUtils.UTF8_CHARSET,
+					blob, 3, blob.length);
+		} else {
+			decoded = RawParseUtils.decode(blob);
+		}
+		fromText(decoded);
 	}
 
 	/**