merge: make debug output slightly more helpful by including message for action

Make recently introduced messages more useful. Instead of:
  f1: g
  f2: m
say:
  f1: remote is newer -> g
  f2: versions differ -> m

mercurial/merge.py

@@ -762,8 +762,8 b' def calculateupdates(repo, wctx, mctx, a'
                                     branchmerge, force,
                                     partial, acceptremote, followcopies)
             for a in sorted(actions):
-                repo.ui.debug(' %s: %s\n' % (a[0], a[1]))
-                f = a[0]
+                f, m, args, msg = a
+                repo.ui.debug(' %s: %s -> %s\n' % (f, msg, m))
                 if f in fbids:
                     fbids[f].append(a)
                 else:

tests/test-merge-criss-cross.t

@@ -135,16 +135,16 b' Redo merge with merge.preferancestor="*"'
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: 3b08d01b0ab5+, remote: adfe50279922
-   f1: g
-   f2: m
+   f1: remote is newer -> g
+   f2: versions differ -> m
   
   calculating bids for ancestor 40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 40663881a6dd, local: 3b08d01b0ab5+, remote: adfe50279922
-   f1: m
-   f2: k
+   f1: versions differ -> m
+   f2: keep -> k
   
   auction for merging merge bids
    f1: picking 'get' action
@@ -180,16 +180,16 b' The other way around:'
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: adfe50279922+, remote: 3b08d01b0ab5
-   f1: k
-   f2: m
+   f1: keep -> k
+   f2: versions differ -> m
   
   calculating bids for ancestor 40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 40663881a6dd, local: adfe50279922+, remote: 3b08d01b0ab5
-   f1: m
-   f2: g
+   f1: versions differ -> m
+   f2: remote is newer -> g
   
   auction for merging merge bids
    f1: picking 'keep' action
@@ -246,16 +246,16 b' Verify how the output looks and and how '
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 0f6b37dbe527, local: 3b08d01b0ab5+, remote: adfe50279922
-   f1: g
-   f2: m
+   f1: remote is newer -> g
+   f2: versions differ -> m
   
   calculating bids for ancestor 40663881a6dd
     searching for copies back to rev 3
   resolving manifests
    branchmerge: True, force: False, partial: False
    ancestor: 40663881a6dd, local: 3b08d01b0ab5+, remote: adfe50279922
-   f1: m
-   f2: k
+   f1: versions differ -> m
+   f2: keep -> k
   
   auction for merging merge bids
    f1: picking 'get' action