Ensures Haskell's leftAlt isn't part of lexeme.

From the report(s):

    An ordinary comment begins with a sequence of two or more consecutive dashes
    (e.g. --) and extends to the following newline. The sequence of dashes must
    not form part of a legal lexeme. For example, “-->” or “|--” do not begin a
    comment, because both of these are legal lexemes; however “--foo” does start
    a comment.

                            Haskell98:   http://goo.gl/CucLL
                            Haskell2010: http://goo.gl/1OYzN

plugin/NERD_commenter.vim

@@ -179,7 +179,7 @@ let s:delimiterMap = {
     \ 'groovy': { 'left': '//', 'leftAlt': '/*', 'rightAlt': '*/' },
     \ 'gsp': { 'left': '<%--', 'right': '--%>', 'leftAlt': '<!--','rightAlt': '-->'},
     \ 'gtkrc': { 'left': '#' },
-    \ 'haskell': { 'left': '{-','right': '-}', 'leftAlt': '--' },
+    \ 'haskell': { 'left': '{-','right': '-}', 'leftAlt': '-- ' },
     \ 'hb': { 'left': '#' },
     \ 'h': { 'left': '//', 'leftAlt': '/*', 'rightAlt': '*/' },
     \ 'haml': { 'left': '-#', 'leftAlt': '/' },