httpserver: Set default idle timeout of 5 minutes (closes #1733)

Also clarified a comment in SiteConfig

caddyhttp/httpserver/server.go

@@ -461,9 +461,9 @@ func (s *Server) OnStartupComplete() {
 }
 
 // defaultTimeouts stores the default timeout values to use
-// if left unset by user configuration. NOTE: Default timeouts
-// are disabled (see issue #1464).
-var defaultTimeouts Timeouts
+// if left unset by user configuration. NOTE: Most default
+// timeouts are disabled (see issues #1464 and #1733).
+var defaultTimeouts = Timeouts{IdleTimeout: 5 * time.Minute}
 
 // tcpKeepAliveListener sets TCP keep-alive timeouts on accepted
 // connections. It's used by ListenAndServe and ListenAndServeTLS so

caddyhttp/httpserver/siteconfig.go

@@ -53,7 +53,8 @@ type SiteConfig struct {
 	// websockets, etc.
 	Timeouts Timeouts
 
-	// If true all unmatched requests will be served by this site
+	// If true, any requests not matching other site definitions
+	// may be served by this site.
 	FallbackSite bool
 }