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/option.h b/src/option.h
index d408a2d..09c044e 100644
--- a/src/option.h
+++ b/src/option.h
@@ -751,7 +751,7 @@
 /* Also used for 'viewoptions'! */
 static char *(p_ssop_values[]) = {"buffers", "winpos", "resize", "winsize",
     "localoptions", "options", "help", "blank", "globals", "slash", "unix",
-    "sesdir", "curdir", "folds", "cursor", "tabpages", NULL};
+    "sesdir", "curdir", "folds", "cursor", "tabpages", "terminal", NULL};
 # endif
 # define SSOP_BUFFERS		0x001
 # define SSOP_WINPOS		0x002
@@ -769,6 +769,7 @@
 # define SSOP_FOLDS		0x2000
 # define SSOP_CURSOR		0x4000
 # define SSOP_TABPAGES		0x8000
+# define SSOP_TERMINAL		0x10000
 #endif
 EXTERN char_u	*p_sh;		/* 'shell' */
 EXTERN char_u	*p_shcf;	/* 'shellcmdflag' */