Don't throw if a pre-push hook is ignored.

This breaks any scenario where native git (with LFS) clones a repository
(and thus installs the hook) and later on JGit is used to push changes.

Change-Id: I2a17753377265a0b612ba3451b9df63a577a1c38
Signed-off-by: Markus Duft <markus.duft@ssi-schaefer.com>

org.eclipse.jgit/src/org/eclipse/jgit/hooks/Hooks.java

@@ -115,7 +115,11 @@ public class Hooks {
 					outputStream);
 			if (hook != null) {
 				if (hook.isNativeHookPresent()) {
-					throw new IllegalStateException(MessageFormat
+					PrintStream ps = outputStream;
+					if (ps == null) {
+						ps = System.out;
+					}
+					ps.println(MessageFormat
 							.format(JGitText.get().lfsHookConflict, repo));
 				}
 				return hook;