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.

bool.h

@@ -0,0 +1,85 @@
+/*
+ * bool - calc standard truth :-)
+ *
+ * Copyright (C) 2023  David I. Bell and Landon Curt Noll
+ *
+ * Primary author:  David I. Bell
+ *
+ * Calc is open software; you can redistribute it and/or modify it under
+ * the terms of the version 2.1 of the GNU Lesser General Public License
+ * as published by the Free Software Foundation.
+ *
+ * Calc is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
+ * Public License for more details.
+ *
+ * A copy of version 2.1 of the GNU Lesser General Public License is
+ * distributed with calc under the filename COPYING-LGPL.  You should have
+ * received a copy with calc; if not, write to Free Software Foundation, Inc.
+ * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ * Under source code control:	2023/07/19 17:58:42
+ * File existed as early as:	1990
+ *
+ * chongo <was here> /\oo/\	http://www.isthe.com/chongo/
+ * Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
+ */
+
+
+#if !defined(INCLUDE_BOOL_H)
+#define INCLUDE_BOOL_H
+
+
+#if defined(HAVE_STDBOOL_H)
+#include <stdbool.h>
+#endif /* HAVE_STDBOOL_H */
+
+
+/*
+ * standard truth :-)
+ */
+#if !defined(__STDC_VERSION__) && (__STDC_VERSION__ >= 199901L)
+
+/* have a C99 compiler - we should have <stdbool.h>, true, false */
+
+#elif !defined(__cplusplus)
+
+/* do not have a C99 compiler - fake a <stdbool.h> header file */
+typedef unsigned char bool;
+#undef true
+#define true ((bool)(1))
+#undef false
+#define false ((bool)(0))
+
+#endif /* standard truth :-) */
+
+
+/*
+ * calc historic booleans
+ */
+#undef TRUE
+#define TRUE	((bool) true)
+#undef FALSE
+#define FALSE	((bool) false)
+#undef BOOL
+#define BOOL bool
+
+
+/*
+ * booltostr - convert a boolean to a string
+ */
+#if !defined(booltostr)
+#define booltostr(x) ((x) ? "true" : "false")
+#endif
+
+
+/*
+ * strtobool - convert a string to a boolean
+ */
+#if !defined(strtobool)
+#define strtobool(x) ((bool) ((x) != NULL && !strcmp((x), "true")))
+#endif
+
+
+#endif /* !INCLUDE_BOOL_H*/