amend: add a flag `-n/--note` to store note with amend

This patch utilises the functionality added in previous patches and adds a flag
to amend command in hgext/amend to add a note to the amend. Since the note is
stored in the obsmarker metadata, this will only be useful when obsmarker
creation is enabled, otherwise this is no-op.

Not adding releasenotes part as we yet don't have a functionality in core to
show the note.

Differential Revision: https://phab.mercurial-scm.org/D1095

hgext/amend.py

@@ -33,6 +33,7 b' command = registrar.command(cmdtable)'
       _('mark new/missing files as added/removed before committing')),
      ('e', 'edit', None, _('invoke editor on commit messages')),
      ('i', 'interactive', None, _('use interactive mode')),
+     ('n', 'note', '', _('store a note on the amend')),
     ] + cmdutil.walkopts + cmdutil.commitopts + cmdutil.commitopts2,
     _('[OPTION]... [FILE]...'),
     inferrepo=True)

tests/test-amend.t

@@ -193,6 +193,14 b' With allowunstable, amend could work in '
   |/
   o  0 426bada5c675 A
   
+Checking the note stored in the obsmarker
+
+  $ echo foo > bar
+  $ hg add bar
+  $ hg amend --note "adding bar"
+  $ hg debugobsolete -r .
+  112478962961147124edd43549aedd1a335e44bf be169c7e8dbe21cd10b3d79691cbe7f241e3c21c 0 (Thu Jan 01 00:00:00 1970 +0000) {'operation': 'amend', 'user': 'test'}
+  be169c7e8dbe21cd10b3d79691cbe7f241e3c21c 16084da537dd8f84cfdb3055c633772269d62e1b 0 (Thu Jan 01 00:00:00 1970 +0000) {'note': 'adding bar', 'operation': 'amend', 'user': 'test'}
 #endif
 
 Cannot amend public changeset