bind: use lowercase method names for Java binds

There was a discussion a year ago about making methods and types
lowercase in ObjC (https://github.com/golang/go/issues/12889),
which was done (https://go-review.googlesource.com/#/c/15780/),
alas the suggested Java lower casing was never addressed.

This CL converts all generated Java methods to lower case.

Change-Id: Ia2f28519bc59362877881636109ddfc651b24960
Reviewed-on: https://go-review.googlesource.com/28494
Reviewed-by: Elias Naur <elias.naur@gmail.com>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/java/Seq.java

@@ -49,12 +49,12 @@ public class Seq {
 	}
 
 	private static void throwException(error err) throws Exception {
-		throw new Exception(err.Error());
+		throw new Exception(err.error());
 	}
 
 	private static error wrapThrowable(final Throwable t) {
 		return new error() {
-			@Override public String Error() {
+			@Override public String error() {
 				return t.getMessage();
 			}
 		};