[PATCH mainline] format: create new repository as 'generaldelta' by default

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1446485598 0
#      Mon Nov 02 17:33:18 2015 +0000
# Node ID 38439322075ccaf7e4bcc2de777c463458f6084b
# Parent  2fb17f60bffa550789b3b95c06ee1577c989cf1d
# EXP-Topic generaldelta
# Available At http://hg.netv6.net/marmoute-wip/mercurial/
#              hg pull http://hg.netv6.net/marmoute-wip/mercurial/ -r 38439322075c
format: create new repository as 'generaldelta' by default

Since we have pushed back the performance issue related to general delta behind
another configuration (Still off by default), we can safely create new
repository with general delta support. As client are compatible with it since
Mercurial 1.9 (4.5 years ago) I do no expect any significant compatibility
issues.

diff --git a/mercurial/help/config.txt b/mercurial/help/config.txt
--- a/mercurial/help/config.txt
+++ b/mercurial/help/config.txt
@@ -668,13 +668,13 @@ Example for ``~/.hgrc``::
 
 ``usegeneraldelta``
     Enable or disable the "generaldelta" repository format which improves
     repository compression by allowing "revlog" to store delta against arbitrary
     revision instead of the previous stored one. This provides significant
-    improvement for repositories with branches. Disabling this option ensures that
-    the on-disk format of newly created repository will be compatible with
-    Mercurial before version 1.9.
+    improvement for repositories with branches. Enabled by default. Disabling
+    this option ensures that the on-disk format of newly created repository will
+    be compatible with Mercurial before version 1.9.
 
 ``usestore``
     Enable or disable the "store" repository format which improves
     compatibility with systems that fold case or otherwise mangle
     filenames. Enabled by default. Disabling this option will allow
diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -1174,11 +1174,11 @@ def wlocksub(repo, cmd, *args, **kwargs)
 def gdinitconfig(ui):
     """helper function to know if a repo should be created as general delta
     """
     # experimental config: format.generaldelta
     return (ui.configbool('format', 'generaldelta', False)
-            or ui.configbool('format', 'usegeneraldelta', False))
+            or ui.configbool('format', 'usegeneraldelta', True))
 
 def gddeltaconfig(ui):
     """helper function to know if incoming delta should be optimised
     """
     # experimental config: format.generaldelta