Created new Conn.Flush() public method so the fd pipeline can be drained arbitrarily by the user.

Commented both flush methods so people know what they are looking at.

This is a necessary fix for streaming and long polling HTTP services.
Fixes #93.

R=r, rsc, david.titarenco
https://golang.org/cl/154099

src/pkg/http/server.go

@@ -238,7 +238,7 @@ func errorKludge(c *Conn, req *Request) {
 	}
 }
 
-func (c *Conn) flush() {
+func (c *Conn) finishRequest() {
 	if !c.wroteHeader {
 		c.WriteHeader(StatusOK)
 	}
@@ -251,6 +251,14 @@ func (c *Conn) flush() {
 	c.buf.Flush();
 }
 
+// Flush sends any buffered data to the client.
+func (c *Conn) Flush() {
+	if !c.wroteHeader {
+		c.WriteHeader(StatusOK)
+	}
+	c.buf.Flush();
+}
+
 // Close the connection.
 func (c *Conn) close() {
 	if c.buf != nil {
@@ -277,7 +285,7 @@ func (c *Conn) serve() {
 		if c.hijacked {
 			return
 		}
-		c.flush();
+		c.finishRequest();
 		if c.closeAfterReply {
 			break
 		}