zcrypto

pull ztools from zgrab (#111)

tls: add tls.Config option to disable buffered handshakes (#105)

Backport most of https://github.com/golang/go/commit/2a8c81ffaadc69add6ff85b241691adb7f9f24ff (only things missing are [1] the change involving bytesSent, which we don't track, and [2] the TestFailedWrite change, since we don't have a TestFailedWrite). (#104)