releasenotes: add pager support when printing to the ui

Differential Revision: https://phab.mercurial-scm.org/D1098

hgext/releasenotes.py

@@ -577,6 +577,7 def releasenotes(ui, repo, file_=None, *
     incoming = parsenotesfromrevisions(repo, sections.names(), revs)
 
     if file_ is None:
+        ui.pager('releasenotes')
         return ui.write(serializenotes(sections, incoming))
 
     try: