conn.Close is not Idempotent

[ganesh-karthick]

API conn.Close() Calling conn.Close on already closed connection causes program to panic, It would be good, if the call is made idempotent.

goroutine 8 [running]:
panic(0x576420, 0xc420252880)
	Documents/devtools/go/src/runtime/panic.go:500 +0x1a1
/github.com/samuel/go-zookeeper/zk.(*Conn).Close(0xc4203ea000)
	/home/Documents/git/goworkspace/src/github.com/samuel/go-zookeeper/zk/conn.go:253 +0x47

[mattn]

any update on this? conn.Close() is not atomic even though most of APIs are goroutine safe.