Fix formatting of #-only lines in herecomments

Before:

    $ ./bin/coffee -bpe '###
    > # paragraph 1
    > #
    > # paragraph 2
    > ###'
    /*
     * paragraph 1
    #
     * paragraph 2
     */

After:

    $ ./bin/coffee -bpe '###
    # paragraph 1
    #
    # paragraph 2
    ###'
    /*
     * paragraph 1
     *
     * paragraph 2
     */

This does not re-break #3638:

    $ ./bin/coffee -bpe '###
    > #/
    > ###'
    /*
    #/
     */

Author: lydell

lib/coffee-script/nodes.js

@@ -584,7 +584,7 @@ exports.Comment = class Comment extends Base
   makeReturn:      THIS
 
   compileNode: (o, level) ->
-    comment = @comment.replace /^(\s*)# /gm, "$1 * "
+    comment = @comment.replace /^(\s*)#(?=\s)/gm, "$1 *"
     code = "/*#{multident comment, @tab}#{if '\n' in comment then "\n#{@tab}" else ''} */"
     code = o.indent + code if (level or o.level) is LEVEL_TOP
     [@makeCode("\n"), @makeCode(code)]