Bug-fix: xpTimeZone_local() returned the UTC-offset as they daylight saving

time was in effect, year-round, on Linux.

Use the localtime() tm_gmtoff method of detecting the local time zone offset
on Linux, don't rely on the global variables 'timezone' and 'daylight'
behaving as they did in Borland C/DOS. From the Linux man page:
 Note that the variable daylight does not indicate that daylight  saving
       time  applies  right now.

src/xpdev/xpdatetime.c

@@ -87,7 +87,7 @@ xpDateTime_t DLLCALL xpDateTime_now(void)
 /* Return local timezone offset (in minutes) */
 xpTimeZone_t DLLCALL xpTimeZone_local(void)
 {
-#if defined(__NetBSD__) || defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__DARWIN__)
+#if defined(__NetBSD__) || defined(__OpenBSD__) || defined(__FreeBSD__) || defined(__DARWIN__) || defined(__linux__)
 	struct tm tm;
 	time_t t;