man: sort options without "=" in the directives index

Some options would appear twice in the index, e.g. --collect= and
--collect. Some man pages use one form, some the other, and the argument
might be mandatory for some commands but not others. Anyway, let's display
them as one entry, to reduce the total number of items listed.

tools/make-directive-index.py

@@ -187,6 +187,9 @@ def _extract_directives(directive_groups, formatting, page):
                              storvar if klass else storopt)):
             for name in variablelist.iterfind(xpath):
                 text = re.sub(r'([= ]).*', r'\1', name.text).rstrip()
+                if text.startswith('-'):
+                    # for options, merge options with and without mandatory arg
+                    text = text.partition('=')[0]
                 stor[text].append((pagename, section))
                 if text not in formatting:
                     # use element as formatted display