commit: use separate variable for p1 manifest and new manifest

In localrepo.commitctx(), p1's manifest is copied and used as the
basis for the manifest that is about to be committed. The way the copy
is updated makes it safe to use it where the original p1's manifest is
wanted. For readability, though, a separate variable for each purpose
would be clearer. Make it so.

mercurial/localrepo.py

@@ -1387,8 +1387,9 b' class localrepository(object):'
             trp = weakref.proxy(tr)
 
             if ctx.files():
-                m1 = p1.manifest().copy()
+                m1 = p1.manifest()
                 m2 = p2.manifest()
+                m = m1.copy()
 
                 # check in files
                 new = {}
@@ -1404,7 +1405,7 b' class localrepository(object):'
                         else:
                             new[f] = self._filecommit(fctx, m1, m2, linkrev,
                                                       trp, changed)
-                            m1.set(f, fctx.flags())
+                            m.set(f, fctx.flags())
                     except OSError, inst:
                         self.ui.warn(_("trouble committing %s!\n") % f)
                         raise
@@ -1415,13 +1416,14 b' class localrepository(object):'
                         raise
 
                 # update manifest
-                m1.update(new)
+                m.update(new)
                 removed = [f for f in sorted(removed) if f in m1 or f in m2]
-                drop = [f for f in removed if f in m1]
+                drop = [f for f in removed if f in m]
                 for f in drop:
-                    del m1[f]
-                mn = self.manifest.add(m1, trp, linkrev, p1.manifestnode(),
-                                       p2.manifestnode(), new, drop)
+                    del m[f]
+                mn = self.manifest.add(m, trp, linkrev,
+                                       p1.manifestnode(), p2.manifestnode(),
+                                       new, drop)
                 files = changed + removed
             else:
                 mn = p1.manifestnode()