spin: Update to most recent version. (thanks Ori_B)

from Ori_B:

There were a small number of changes needed from the tarball
on spinroot.org:

  - The mkfile needed to be updated
  - Memory.h needed to not be included
  - It needed to invoke /bin/cpp instead of gcc -E
  - It depended on `yychar`, which our yacc doesn't
    provide.

I'm still figuring out how to use spin, but it seems to do
the right thing when testing a few of the examples:

	% cd $home/src/Spin/Examples/
	% spin -a peterson.pml
	% pcc pan.c -D_POSIX_SOURCE
	% ./6.out

	(Spin Version 6.4.7 -- 19 August 2017)
		+ Partial Order Reduction

	Full statespace search for:
		never claim         	- (none specified)
		assertion violations	+
		acceptance   cycles 	- (not selected)
		invalid end states	+

	State-vector 32 byte, depth reached 24, errors: 0
	40 states, stored
	27 states, matched
	67 transitions (= stored+matched)
		0 atomic steps
	hash conflicts:         0 (resolved)

	Stats on memory usage (in Megabytes):
	0.002	equivalent memory usage for states (stored*(State-vector + overhead))
	0.292	actual memory usage for states
	128.000	memory used for hash table (-w24)
	0.534	memory used for DFS stack (-m10000)
	128.730	total actual memory usage


	unreached in proctype user
		/tmp/Spin/Examples/peterson.pml:20, state 10, "-end-"
		(1 of 10 states)

	pan: elapsed time 1.25 seconds
	pan: rate        32 states/second

1 files changed, 23 insertions, 13 deletions

diff --git a/sys/src/cmd/spin/tl_parse.c b/sys/src/cmd/spin/tl_parse.c
index 6206a0d99..6a16017ec 100644
--- a/sys/src/cmd/spin/tl_parse.c
+++ b/sys/src/cmd/spin/tl_parse.c
@@ -1,16 +1,13 @@
 /***** tl_spin: tl_parse.c *****/
 
-/* Copyright (c) 1995-2003 by Lucent Technologies, Bell Laboratories.     */
-/* All Rights Reserved.  This software is for educational purposes only.  */
-/* No guarantee whatsoever is expressed or implied by the distribution of */
-/* this code.  Permission is given to distribute this code provided that  */
-/* this introductory message is not removed and no monies are exchanged.  */
-/* Software written by Gerard J. Holzmann.  For tool documentation see:   */
-/*             http://spinroot.com/                                       */
-/* Send all bug-reports and/or questions to: bugs@spinroot.com            */
-
-/* Based on the translation algorithm by Gerth, Peled, Vardi, and Wolper, */
-/* presented at the PSTV Conference, held in 1995, Warsaw, Poland 1995.   */
+/*
+ * This file is part of the public release of Spin. It is subject to the
+ * terms in the LICENSE file that is included in this source directory.
+ * Tool documentation is available at http://spinroot.com
+ *
+ * Based on the translation algorithm by Gerth, Peled, Vardi, and Wolper,
+ * presented at the PSTV Conference, held in 1995, Warsaw, Poland 1995.
+ */
 
 #include "tl.h"
 
@@ -44,11 +41,13 @@ tl_factor(void)
 		ptr = tl_yylval;
 		tl_yychar = tl_yylex();
 		ptr->lft = tl_factor();
+		if (!ptr->lft)
+		{	fatal("malformed expression", (char *) 0);
+		}
 		ptr = push_negation(ptr);
 		break;
 	case ALWAYS:
 		tl_yychar = tl_yylex();
-
 		ptr = tl_factor();
 #ifndef NO_OPT
 		if (ptr->ntyp == FALSE
@@ -73,6 +72,14 @@ tl_factor(void)
 		ptr = tl_nn(NEXT, ptr, ZN);
 		break;
 #endif
+	case CEXPR:
+		tl_yychar = tl_yylex();
+		ptr = tl_factor();
+		if (ptr->ntyp != PREDICATE)
+		{	tl_yyerror("expected {...} after c_expr");
+		}
+		ptr = tl_nn(CEXPR, ptr, ZN);
+		break;
 	case EVENTUALLY:
 		tl_yychar = tl_yylex();
 
@@ -385,7 +392,10 @@ tl_formula(void)
 
 void
 tl_parse(void)
-{	Node *n = tl_formula();
+{	Node *n;
+
+	/* tl_verbose = 1; */
+	n = tl_formula();
 	if (tl_verbose)
 	{	printf("formula: ");
 		dump(n);