enable merge commits by default

fixes #4309

Author: vladak

opengrok-indexer/src/main/java/org/opengrok/indexer/configuration/Configuration.java

@@ -585,7 +585,7 @@ public Configuration() {
         //mandoc is default(String)
         setMaxSearchThreadCount(2 * Runtime.getRuntime().availableProcessors());
         setMaxRevisionThreadCount(Runtime.getRuntime().availableProcessors());
-        setMergeCommitsEnabled(false);
+        setMergeCommitsEnabled(true);
         setMessageLimit(500);
         setNavigateWindowEnabled(false);
         setNestingMaximum(1);