Placeables: Skip non-placeholders with whitespace

This fix prevents from detecting strings like "% s" to be format placeholders.

Fixes translate#3368.

translate/storage/placeables/general.py

@@ -157,7 +157,7 @@ class FormattingPlaceable(Ph):
     regex = re.compile(r"""
         %                         # introduction
         (\d+\$)?                  # selection of non-next variable (reordering)
-        [\-\+0 \#'I]?             # optional flag
+        [\-\+0\#'I]?              # optional flag
         ((\d+)|[*])?              # field width
         (\.\d+)?                  # precision
         [hlI]?                    # length

translate/storage/placeables/test_general.py

@@ -102,7 +102,10 @@ def test_placeable_formatting():
     assert fp.parse(u'There were %d %s')[3] == fp([u'%s'])
     assert fp.parse(u'%1$s was kicked by %2$s')[0] == fp([u'%1$s'])
     assert fp.parse(u'There were %Id cows')[1] == fp([u'%Id'])
-    assert fp.parse(u'There were % d cows')[1] == fp([u'% d'])
+
+    # Skip placeholders with whitespace.
+    assert fp.parse(u'There were % d cows') is None
+
     # only a real space is allowed as formatting flag
     assert fp.parse(u'There were %\u00a0d cows') is None
     assert fp.parse(u"There were %'f cows")[1] == fp([u"%'f"])