go.crypto/ssh/terminal: Allow ^A and ^E as synonyms for Home and End.

I understand that ssh/terminal can't implement everybodys
favorite keyboard shortcuts, but I think these are very
widespread. They exist not only in Emacs or Readline, but also
in Acme and Sam. Also they almost come for free.

R=golang-dev
CC=agl, golang-dev
https://golang.org/cl/13839047

terminal.go

@@ -132,6 +132,10 @@ func bytesToKey(b []byte) (rune, []byte) {
 	}
 
 	switch b[0] {
+	case 1: // ^A
+		return keyHome, b[1:]
+	case 5: // ^E
+		return keyEnd, b[1:]
 	case 8: // ^H
 		return keyBackspace, b[1:]
 	case 11: // ^K

terminal_test.go

@@ -101,6 +101,18 @@ var keyPressTests = []struct {
 		line:           "line1xxx",
 		throwAwayLines: 2,
 	},
+	{
+		// Ctrl-A to move to beginning of line followed by ^K to kill
+		// line.
+		in:   "a b \001\013\r",
+		line: "",
+	},
+	{
+		// Ctrl-A to move to beginning of line, Ctrl-E to move to end,
+		// finally ^K to kill nothing.
+		in:   "a b \001\005\013\r",
+		line: "a b ",
+	},
 	{
 		in:   "\027\r",
 		line: "",