Fix up parent display in logging

For changesets with a first parent nullid, but not rev 0, we ought to
display a null parent.

mercurial/commands.py

@@ -324,12 +324,13 b' class changeset_printer(object):'
 
         parents = log.parentrevs(rev)
         if not self.ui.debugflag:
-            parents = [p for p in parents if p != nullrev]
-            if len(parents) == 1 and parents[0] == rev-1:
+            if parents[1] == nullrev:
+                if parents[0] >= rev - 1:
                 parents = []
+                else:
+                    parents = [parents[0]]
         parents = [(p, hexfunc(log.node(p))) for p in parents]
 
-
         self.ui.write(_("changeset:   %d:%s\n") % (rev, hexfunc(changenode)))
 
         if branch:

tests/test-globalopts.out

@@ -27,6 +27,7 b' summary: b'
 %% abbrev of long option
 changeset:   1:b6c483daf290
 tag:         tip
+parent:      -1:000000000000
 user:        test
 date:        Thu Jan 01 00:00:01 1970 +0000
 summary:     b
@@ -49,6 +50,7 b' 1:b6c483daf290'
 %% -v/--verbose
 changeset:   1:b6c483daf290
 tag:         tip
+parent:      -1:000000000000
 user:        test
 date:        Thu Jan 01 00:00:01 1970 +0000
 files:       b

tests/test-unrelated-pull.out

@@ -11,6 +11,7 b' added 1 changesets with 1 changes to 1 f'
 (run 'hg heads' to see heads, 'hg merge' to merge)
 changeset:   1:bdcee5d51fa6
 tag:         tip
+parent:      -1:000000000000
 user:        a
 date:        Mon Jan 12 13:46:40 1970 +0000
 summary:     a