Add toString to GitMerge/RebaseUpdater for nicer logging.

plugins/git4idea/src/git4idea/update/GitMergeUpdater.java

@@ -245,6 +245,11 @@ public class GitMergeUpdater extends GitUpdater {
     return changes;
   }
 
+  @Override
+  public String toString() {
+    return "Merge updater";
+  }
+
   private enum MergeError {
     CONFLICT,
     LOCAL_CHANGES,

plugins/git4idea/src/git4idea/update/GitRebaseUpdater.java

@@ -154,6 +154,11 @@ public class GitRebaseUpdater extends GitUpdater {
     return !cancelled.get();
   }
 
+  @Override
+  public String toString() {
+    return "Rebase updater";
+  }
+
   private static class MyConflictResolver extends GitConflictResolver {
     private final GitRebaser myRebaser;
     private final VirtualFile myRoot;