templatekw: reorder stub of showparents() function

It will have an implementation.

mercurial/templatekw.py

@@ -397,6 +397,12 b' def showp2node(repo, ctx, templ, **args)'
     parent, all digits are 0."""
     return ctx.p2().hex()
 
+def _showparents(**args):
+    """:parents: List of strings. The parents of the changeset in "rev:node"
+    format. If the changeset has only one "natural" parent (the predecessor
+    revision) nothing is shown."""
+    pass
+
 def showphase(repo, ctx, templ, **args):
     """:phase: String. The changeset phase name."""
     return ctx.phasestr()
@@ -492,12 +498,6 b' keywords = {'
     'tags': showtags,
 }
 
-def _showparents(**args):
-    """:parents: List of strings. The parents of the changeset in "rev:node"
-    format. If the changeset has only one "natural" parent (the predecessor
-    revision) nothing is shown."""
-    pass
-
 dockeywords = {
     'parents': _showparents,
 }