minirst: modified minirst to also recognize empty comments.

The modifies minirst to also handle empty comments. An empty comment
is a block with a single line containing two dots.

mercurial/minirst.py

@@ -278,7 +278,8 b' def prunecomments(blocks):'
     i = 0
     while i < len(blocks):
         b = blocks[i]
-        if b['type'] == 'paragraph' and b['lines'][0].startswith('.. '):
+        if b['type'] == 'paragraph' and (b['lines'][0].startswith('.. ') or
+                                         b['lines'] == ['..']):
             del blocks[i]
             if i < len(blocks) and blocks[i]['type'] == 'margin':
                 del blocks[i]

tests/test-minirst.py

@@ -221,6 +221,10 b' Some text.'
    .. An indented comment
 
    Some indented text.
+
+..
+
+Empty comment above
 """
 
 debugformat('comments', comments, 30)

tests/test-minirst.py.out

@@ -339,5 +339,7 b' comments formatted to fit within 30 char'
 Some text.
 
    Some indented text.
+
+Empty comment above
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