Avoid escaping some chars in po files

These really do not have to be escaped in the po file, so keep them as
they are.

translate/storage/pocommon.py

@@ -42,7 +42,7 @@ def extract_msgid_comment(text):
 
 def quote_plus(text):
     """Quote the query fragment of a URL; replacing ' ' with '+'"""
-    return parse.quote_plus(text.encode("utf-8"))
+    return parse.quote_plus(text.encode("utf-8"), safe='()/:,')
 
 
 def unquote_plus(text):

translate/storage/test_pocommon.py

@@ -1,4 +1,5 @@
 # -*- coding: utf-8 -*-
+from __future__ import unicode_literals
 
 from translate.storage import pocommon
 
@@ -10,6 +11,10 @@ def roundtrip_quote_plus(text, quoted):
         assert quote == quoted
         unquote = pocommon.unquote_plus(quoted)
         assert unquote == text
-    roundtrip_quote_plus(u"abc", u"abc")
-    roundtrip_quote_plus(u"key space", u"key+space")
-    roundtrip_quote_plus(u"key ḓey", u"key+%E1%B8%93ey")
+    roundtrip_quote_plus("abc", "abc")
+    roundtrip_quote_plus("key space", "key+space")
+    roundtrip_quote_plus("key ḓey", "key+%E1%B8%93ey")
+    roundtrip_quote_plus(
+        "path/file.c(2):3,path space/file.h:4",
+        "path/file.c(2):3,path+space/file.h:4"
+    )