changed C source to use C booleans with backward compatibility

Fix "Under source code control" date for new version.h file.

Sorted the order of symbols printed by "make env".

Test if <stdbool.h> exists and set HAVE_STDBOOL_H accordingly
in have_stdbool.h.  Added HAVE_STDBOOL_H to allow one to force
this value.

Added "bool.h" include file to support use of boolean symbols,
true and false for pre-c99 C compilers.  The "bool.h" include
file defines TRUE as true, FALSE as false, and BOOL as bool:
for backward compatibility.

The sign in a ZVALUE is now of type SIGN, whcih is either
SB32 when CALC2_COMPAT is defined, or a bool.

Replaced in C source, TRUE with true, FALSE with false, and
BOOL with bool.

symbol.c

@@ -1,7 +1,7 @@
 /*
  * symbol - global and local symbol routines
  *
- * Copyright (C) 1999-2007,2021,2022  David I. Bell and Ernest Bowen
+ * Copyright (C) 1999-2007,2021-2023  David I. Bell and Ernest Bowen
  *
  * Primary author:  David I. Bell
  *
@@ -89,10 +89,10 @@ initglobals(void)
  *
  * given:
  *	name		name of global variable
- *	isstatic	TRUE if symbol is static
+ *	isstatic	true if symbol is static
  */
 GLOBAL *
-addglobal(char *name, BOOL isstatic)
+addglobal(char *name, bool isstatic)
 {
 	GLOBAL *sp;		/* current symbol pointer */
 	GLOBAL **hp;		/* hash table head address */
@@ -493,7 +493,7 @@ exitfuncscope(void)
  * variable is at the same file and function level.
  */
 void
-endscope(char *name, BOOL isglobal)
+endscope(char *name, bool isglobal)
 {
 	GLOBAL *sp;
 	GLOBAL *prevsp;