[PATCH 1 of 4 V2] revert: small refactoring in the way backup value are handled

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1409358507 -7200
#      Sat Aug 30 02:28:27 2014 +0200
# Node ID 5ddd515bd5209e36ccc0cc40d9e8436253bc611b
# Parent  4109cc16279ef0e04dc70e7f4c9ab7415e6a22d3
revert: small refactoring in the way backup value are handled

The current backup value may have two different values:

  1. Do not try to do backup
  2. Do backup if applicable

We are about to move to:

  1. Do not try to do backup
  2. Do backup if applicable
  3. Do backup in all cases

So we change the current values to make room for the new one.

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -2615,14 +2615,17 @@ def revert(ui, repo, ctx, parents, *pats
                    'undelete': ([], _('undeleting %s\n')),
                    'noop': (None, _('no changes needed to %s\n')),
                    'unknown': (None, _('file not managed: %s\n')),
                   }
 
-
-        # should we do a backup?
-        backup = not opts.get('no_backup')
-        discard = False
+        # "constant" that convey the backup strategy.
+        # All set to `discard` if `no-backup` is set do avoid checking
+        # no_backup lower in the code.
+        backup = 2  # unconditionnally do backup
+        discard = 0 # never do backup
+        if opts.get('no_backup'):
+            backup = discard
 
         disptable = (
             # dispatch table:
             #   file state
             #   action