Change line commenting to ignore blanks if any non-blanks

Fixes #2526

This slightly alters the heuristic for deciding whether to uncomment
or to comment blocks of code. Previously, it would key off the first
line of code and only if that was commented would it check the other
lines. Now it checks all lines of code and uncomments the block if all
non-blank lines are commented out.

src/language-mode.coffee

@@ -41,9 +41,9 @@ class LanguageMode
     buffer = @editor.buffer
     commentStartRegexString = _.escapeRegExp(commentStartString).replace(/(\s+)$/, '(?:$1)?')
     commentStartRegex = new OnigRegExp("^(\\s*)(#{commentStartRegexString})")
-    shouldUncomment = commentStartRegex.test(buffer.lineForRow(start))
 
     if commentEndString
+      shouldUncomment = commentStartRegex.test(buffer.lineForRow(start))
       if shouldUncomment
         commentEndRegexString = _.escapeRegExp(commentEndString).replace(/^(\s+)/, '(?:$1)?')
         commentEndRegex = new OnigRegExp("(#{commentEndRegexString})(\\s*)$")
@@ -64,10 +64,18 @@ class LanguageMode
           buffer.insert([start, indentLength], commentStartString)
           buffer.insert([end, buffer.lineLengthForRow(end)], commentEndString)
     else
-      if shouldUncomment and start isnt end
-        shouldUncomment = [start+1..end].every (row) ->
-          line = buffer.lineForRow(row)
-          not line or commentStartRegex.test(line)
+      blankRegex = new OnigRegExp("^\\s*$")
+
+      allBlank = true
+      allBlankOrCommented = [start..end].every (row) ->
+        line = buffer.lineForRow(row)
+        blank = not line or blankRegex.test(line)
+
+        allBlank = allBlank and blank
+        blank or commentStartRegex.test(line)
+
+      shouldUncomment = allBlankOrCommented and not allBlank
+
       if shouldUncomment
         for row in [start..end]
           if match = commentStartRegex.search(buffer.lineForRow(row))