add suggests: php5-curl to tt-rss-common (fixes #407)

debian/control

@@ -9,6 +9,7 @@ Homepage: http://tt-rss.org/
 Package: tt-rss-common
 Architecture: any
 Depends: php5, ${misc:Depends}
+Suggests: php5-curl
 Description: Tiny Tiny RSS is a web-based news feed (RSS/Atom)
  aggregator, designed to allow you to read news from any location,
  while feeling as close to a real desktop application as possible.