Don't try to uncompress .Z files when saving them. Bug 162271, patch by harm

ten Napel <harm.ten.napel@oracle.com> and Smaug <smaug@jippii.fi>, r=dwitte,
sr=bzbarsky, a=dbaron

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -157,6 +157,7 @@ static const char* const nonDecodableTypes [] = {
 static const char* const nonDecodableExtensions [] = {
   "gz",
   "zip",
+  "Z",
   0
 };