obsmarker: rename precnode into prednode

obsmarker: rename precnode into prednode

Rename prednode (predecessors node) into precnode (precursors node) in markers
class. Use util.nouideprecwarn because markers doesn't have easy access to an
ui object.

The renaming is done according to
https://www.mercurial-scm.org/wiki/CEDVocabulary.

Differential Revision: https://phab.mercurial-scm.org/D243

--- a/mercurial/cmdutil.py	Wed Aug 02 19:13:56 2017 +0200
+++ b/mercurial/cmdutil.py	Wed Aug 02 19:20:59 2017 +0200
@@ -1913,7 +1913,7 @@
     To be used by debug function."""
     if index is not None:
         fm.write('index', '%i ', index)
-    fm.write('precnode', '%s ', hex(marker.precnode()))
+    fm.write('precnode', '%s ', hex(marker.prednode()))
     succs = marker.succnodes()
     fm.condwrite(succs, 'succnodes', '%s ',
                  fm.formatlist(map(hex, succs), name='node'))

--- a/mercurial/obsutil.py	Wed Aug 02 19:13:56 2017 +0200
+++ b/mercurial/obsutil.py	Wed Aug 02 19:20:59 2017 +0200
@@ -9,6 +9,7 @@
 
 from . import (
     phases,
+    util
 )
 
 class marker(object):
@@ -29,7 +30,13 @@
         return self._data == other._data
 
     def precnode(self):
-        """Precursor changeset node identifier"""
+        msg = ("'marker.precnode' is deprecated, "
+               "use 'marker.precnode'")
+        util.nouideprecwarn(msg, '4.4')
+        return self.prednode()
+
+    def prednode(self):
+        """Predecessor changeset node identifier"""
         return self._data[0]
 
     def succnodes(self):
@@ -37,7 +44,7 @@
         return self._data[1]
 
     def parentnodes(self):
-        """Parents of the precursors (None if not recorded)"""
+        """Parents of the predecessors (None if not recorded)"""
         return self._data[5]
 
     def metadata(self):