add parsing support for msgctxt field of poitems

The gettext format specifies a msgctxt field for translated items. An
example of how to use this field has been added to the tests and the
parsing of this attribute has been implemented.

lib/po.js

@@ -139,6 +139,10 @@ PO.parse = function (data) {
             item.msgstr[plural] = extract(line);
             context = 'msgstr';
         }
+        else if (line.match(/^msgctxt/)) { // Context
+            finish();
+            item.msgctxt = extract(line);
+        }
         else { // Probably multiline string or blank
             if (line.length > 0) {
                 if (context === 'msgstr') {
@@ -160,6 +164,7 @@ PO.parse = function (data) {
 
 PO.Item = function () {
     this.msgid = '';
+    this.msgctxt = '';
     this.references = [];
     this.msgid_plural = null;
     this.msgstr = [];

test/fixtures/big.po

@@ -285,3 +285,13 @@ msgstr "Attribut 'title' du lien"
 # Comment
 msgid "Title, as plain text"
 msgstr "Attribut title, en tant que texte brut"
+
+# Empty should be adjective
+msgctxt "folder display"
+msgid "Empty folder"
+msgstr "This folder is empty."
+
+# Empty should be verb
+msgctxt "folder action"
+msgid "Empty folder"
+msgstr "Make this folder empty."

test/parse.js

@@ -6,7 +6,7 @@ describe('Parse', function () {
     it('Parses the big po file', function () {
         var po = PO.parse(fs.readFileSync(__dirname + '/fixtures/big.po', 'utf8'));
         assert.notEqual(po, null);
-        assert.equal(po.items.length, 67);
+        assert.equal(po.items.length, 69);
         
         var item = po.items[0];
         assert.equal(item.msgid, "Title");
@@ -62,4 +62,15 @@ describe('Parse', function () {
         assert.notEqual(item.flags, null);
         assert.equal(item.flags.fuzzy, true);
     });
+
+    it('Parses item context', function () {
+        var po = PO.parse(fs.readFileSync(__dirname + '/fixtures/big.po', 'utf8'));
+
+        var ambiguousItems = po.items.filter(function (item) {
+            return item.msgid === 'Empty folder';
+        });
+
+        assert.equal(ambiguousItems[0].msgctxt, 'folder display');
+        assert.equal(ambiguousItems[1].msgctxt, 'folder action');
+    });
 });