patch 8.0.1592: terminal windows in a session are not properly restored

Problem:    Terminal windows in a session are not properly restored.
Solution:   Add "terminal" in 'sessionoptions'.  When possible restore the
            command running in a terminal.
diff --git a/src/proto/terminal.pro b/src/proto/terminal.pro
index 9c29683..aefa40d 100644
--- a/src/proto/terminal.pro
+++ b/src/proto/terminal.pro
@@ -1,5 +1,8 @@
 /* terminal.c */
 void ex_terminal(exarg_T *eap);
+int term_write_session(FILE *fd, win_T *wp);
+int term_should_restore(buf_T *buf);
+void f_term_setrestore(typval_T *argvars, typval_T *rettv);
 void free_terminal(buf_T *buf);
 void write_to_term(buf_T *buffer, char_u *msg, channel_T *channel);
 int term_job_running(term_T *term);