merge: enable defaulttoupstream by default

There's no point in this:

% git merge
fatal: No commit specified and merge.defaultToUpstream not set.

We know the most likely scenario is that the user wants to merge the
upstream, and if not, he can set merge.defaultToUpstream to false.
Signed-off-by: NFelipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-merge.txt

@@ -101,9 +101,8 @@ commit or stash your changes before running 'git merge'.
 	Specifying more than one commit will create a merge with
 	more than two parents (affectionately called an Octopus merge).
 +
-If no commit is given from the command line, and if `merge.defaultToUpstream`
-configuration variable is set, merge the remote-tracking branches
-that the current branch is configured to use as its upstream.
+If no commit is given from the command line, merge the remote-tracking
+branches that the current branch is configured to use as its upstream.
 See also the configuration section of this manual page.
 
 

builtin/merge.c

@@ -63,7 +63,7 @@ static int verbosity;
 static int allow_rerere_auto;
 static int abort_current_merge;
 static int show_progress = -1;
-static int default_to_upstream;
+static int default_to_upstream = 1;
 static const char *sign_commit;
 
 static struct strategy all_strategy[] = {