gendoc: use an empty comment so aliases are separated from previous elements

For commands like `hg bookmarks`, where there's no `[+] marked option can be
specified multiple times`, this causes the final option in the option list to
not be the parent of the aliases definition. The aliases section is thus marked
as a blockquote like on commands that do have text separating the option list
and the aliases definition.

Differential Revision: https://phab.mercurial-scm.org/D9990

doc/gendoc.py

@@ -317,7 +317,12 b' def commandprinter(ui, cmdtable, section'
                 ui.write(b"\n")
             # aliases
             if d[b'aliases']:
-                ui.write(_(b"    aliases: %s\n\n") % b" ".join(d[b'aliases']))
+                # Note the empty comment, this is required to separate this
+                # (which should be a blockquote) from any preceding things (such
+                # as a definition list).
+                ui.write(
+                    _(b"..\n\n    aliases: %s\n\n") % b" ".join(d[b'aliases'])
+                )
 
 
 def allextensionnames():