Fix ExecCommandWith for cmd.exe in Windows (#1072)

Close #1018

Run the command as is in cmd.exe with no parsing and escaping.
Explicity set cmd.SysProcAttr so execCommand does not escape the command.
Technically, the command should be escaped with ^ for special characters,
including ". This allows cmd.exe commands to be chained together.

See https://github.com/neovim/neovim/pull/7343#issuecomment-333350201

This commit also updates quoteEntry to use strings.Replace instead of
strconv.Quote which escapes more than \ and ".

src/terminal.go

@@ -1103,9 +1103,18 @@ func keyMatch(key int, event tui.Event) bool {
 		event.Type == tui.Mouse && key == tui.DoubleClick && event.MouseEvent.Double
 }
 
+func quoteEntryCmd(entry string) string {
+	escaped := strings.Replace(entry, `\`, `\\`, -1)
+	escaped = `"` + strings.Replace(escaped, `"`, `\"`, -1) + `"`
+	r, _ := regexp.Compile(`[&|<>()@^%!"]`)
+	return r.ReplaceAllStringFunc(escaped, func(match string) string {
+		return "^" + match
+	})
+}
+
 func quoteEntry(entry string) string {
 	if util.IsWindows() {
-		return strconv.Quote(strings.Replace(entry, "\"", "\\\"", -1))
+		return quoteEntryCmd(entry)
 	}
 	return "'" + strings.Replace(entry, "'", "'\\''", -1) + "'"
 }