qapi: Avoid unwanted blank lines in QAPIDoc

We silently fix missing #optional tags for QAPIDoc by appending a line
"#optional" to the section's .content.  However, this interferes with
.__repr__ stripping trailing blank lines from .content.

Use new ArgSection instance variable .optional instead, and leave
.content alone.

To permit testing .optional in texi_body(), clean up texi_enum()'s
hack to add empty documentation for undocumented enum values: add an
ArgSection instead of ''.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1489582656-31133-12-git-send-email-armbru@redhat.com>
diff --git a/scripts/qapi2texi.py b/scripts/qapi2texi.py
index 0f3e573..0aaf45c 100755
--- a/scripts/qapi2texi.py
+++ b/scripts/qapi2texi.py
@@ -136,7 +136,7 @@
         for arg, section in doc.args.iteritems():
             desc = str(section)
             opt = ''
-            if "#optional" in desc:
+            if section.optional:
                 desc = re.sub(r'^ *#optional *\n?|\n? *#optional *$|#optional',
                               '', desc)
                 opt = ' (optional)'
@@ -185,7 +185,7 @@
     """Format an enum to texi"""
     for i in expr['data']:
         if i not in doc.args:
-            doc.args[i] = ''
+            doc.args[i] = qapi.QAPIDoc.ArgSection(i)
     body = texi_body(doc)
     return TYPE_FMT(type="Enum",
                     name=doc.symbol,