Don't need hack copy of system() anymore in OS X 10.3.

src/backend/port/darwin/README

@@ -24,3 +24,8 @@ port/SUBSYS.o definition of _system in section (__TEXT,__text)
 /usr/lib/libm.dylib(system.o) unused definition of _system
 
 These are due to overriding system() per the above-described hack.
+
+
+The bug appears to be repaired in OS X 10.2.6 and later (possibly in
+earlier 10.2.* as well, but no systems handy to check).  We #ifdef out
+the substitute system() definition on 10.3 and later.

src/backend/port/darwin/system.c

+/* only needed in OS X 10.1 and possibly early 10.2 releases */
+#include <AvailabilityMacros.h>
+#if MAC_OS_X_VERSION_MAX_ALLOWED <= MAC_OS_X_VERSION_10_2 || !defined(MAC_OS_X_VERSION_10_2)
+
 /*
  * Copyright (c) 1988, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -97,3 +101,5 @@ system(const char *command)
 	(void) sigprocmask(SIG_SETMASK, &oldsigblock, NULL);
 	return (pid == -1 ? -1 : pstat);
 }
+
+#endif /* OS X < 10.3 */