Merge branch 'errstr-for-db' into 'master'

//

//	const char *sqlite3_errstr(int);

func (c *conn) errstr(rc int32) error {

	p := sqlite3.Xsqlite3_errstr(c.tls, rc)

	str := libc.GoString(p)

	p = sqlite3.Xsqlite3_errmsg(c.tls, c.db)

	return errstrForDB(c.tls, rc, c.db)

}

func errstrForDB(tls *libc.TLS, rc int32, db uintptr) error {

	pStr := sqlite3.Xsqlite3_errstr(tls, rc)

	str := libc.GoString(pStr)

	var s string

	if rc == sqlite3.SQLITE_BUSY {

		s = " (SQLITE_BUSY)"

	}

	switch msg := libc.GoString(p); {

	if db == 0 {

		return &Error{msg: fmt.Sprintf("%s (%v)%s", str, rc, s), code: int(rc)}

	}

	pMsg := sqlite3.Xsqlite3_errmsg(tls, db)

	switch msg := libc.GoString(pMsg); {

	case msg == str:

		return &Error{msg: fmt.Sprintf("%s (%v)%s", str, rc, s), code: int(rc)}

	default: