new implementation of items marked obsolete

the current implementation of items marked obsolete did not allow "plain"
comments for these items. However, this is perfectly fine according to
the original gettext tools. When writing a po file, comments for obsolete
items don't contain the '#~ ' mark (tested using msgcat), so this is now
also aligned with the behaviour of the original gettext tools.

For all these cases I added examples in the po files, that failed with the
current implementation and work fine after these changes.

lib/po.js

@@ -101,14 +101,18 @@ PO.parse = function (data) {
     var item = new PO.Item(),
         context = null,
         plural = 0,
-        obsolete = false;
+        obsoleteCount = 0,
+        noCommentLineCount = 0;
 
     function finish() {
         if (item.msgid.length > 0) {
+            if (obsoleteCount >= noCommentLineCount) {
+                item.obsolete = true;
+            }
+            obsoleteCount = 0;
+            noCommentLineCount = 0;
             po.items.push(item);
             item = new PO.Item();
-            item.obsolete = obsolete;
-            obsolete = false;
         }
     }
 
@@ -122,13 +126,15 @@ PO.parse = function (data) {
 
     while (lines.length > 0) {
         var line = trim(lines.shift()),
+            lineObsolete = false,
             add = false;
 
         if (line.match(/^#\~/)) { // Obsolete item
-            obsolete = true;
+            //only remove the obsolte comment mark, here
+            //might be, this is a new item, so
+            //only remember, this line is marked obsolete, count after line is parsed
             line = trim(line.substring(2));
-        } else {
-            obsolete = false;
+            lineObsolete = true;
         }
 
         if (line.match(/^#:/)) { // Reference
@@ -153,24 +159,29 @@ PO.parse = function (data) {
         else if (line.match(/^msgid_plural/)) { // Plural form
             item.msgid_plural = extract(line);
             context = 'msgid_plural';
+            noCommentLineCount++;
         }
         else if (line.match(/^msgid/)) { // Original
             finish();
             item.msgid = extract(line);
             context = 'msgid';
+            noCommentLineCount++;
         }
         else if (line.match(/^msgstr/)) { // Translation
             var m = line.match(/^msgstr\[(\d+)\]/);
             plural = m && m[1] ? parseInt(m[1]) : 0;
             item.msgstr[plural] = extract(line);
             context = 'msgstr';
+            noCommentLineCount++;
         }
         else if (line.match(/^msgctxt/)) { // Context
             finish();
             item.msgctxt = extract(line);
+            noCommentLineCount++;
         }
         else { // Probably multiline string or blank
             if (line.length > 0) {
+                noCommentLineCount++;
                 if (context === 'msgstr') {
                     item.msgstr[plural] += extract(line);
                 }
@@ -182,6 +193,10 @@ PO.parse = function (data) {
                 }
             }
         }
+        if (lineObsolete) {
+            //count obsolete lines for this item
+            obsoleteCount++;
+        }
     }
     finish();
 
@@ -245,27 +260,24 @@ PO.Item.prototype.toString = function () {
     if (flags.length > 0) {
         lines.push('#, ' + flags.join(","));
     }
+    var mkObsolete = this.obsolete ? '#~ ' : '';
 
     ['msgctxt', 'msgid', 'msgid_plural', 'msgstr'].forEach(function (keyword) {
         var text = that[keyword];
         if (text != null) {
             if (isArray(text) && text.length > 1) {
                 text.forEach(function (t, i) {
-                    lines = lines.concat(_process(keyword, t, i));
+                    lines = lines.concat(mkObsolete + _process(keyword, t, i));
                 });
             }
             else {
                 text = isArray(text) ? text.join() : text;
-                lines = lines.concat(_process(keyword, text));
+                lines = lines.concat(mkObsolete + _process(keyword, text));
             }
         }
     });
 
-    if (this.obsolete) {
-        return "#~ " + lines.join("\n#~ ");
-    } else {
-        return lines.join("\n");
-    }
+    return lines.join("\n");
 };
 
 module.exports = PO;