Update Darwin dlopen() support to avoid deprecation warnings with latest

Apple developer tools.  We now use dlopen directly if available, and fall
back to the older code if not.  Chris Campbell

src/backend/port/dynloader/darwin.c

 /*
- * These routines were taken from the Apache source, but were made
- * available with a PostgreSQL-compatible license.	Kudos Wilfredo
- * Snchez <wsanchez@apple.com>.
+ * Dynamic loading support for Darwin
  *
- * $PostgreSQL: pgsql/src/backend/port/dynloader/darwin.c,v 1.10 2004/01/07 18:56:27 neilc Exp $
+ * If dlopen() is available (Darwin 10.3 and later), we just use it.
+ * Otherwise we emulate it with the older, now deprecated, NSLinkModule API.
+ *
+ * $PostgreSQL: pgsql/src/backend/port/dynloader/darwin.c,v 1.11 2006/10/08 19:31:03 tgl Exp $
  */
 #include "postgres.h"
 
+#ifdef HAVE_DLOPEN
+#include <dlfcn.h>
+#else
 #include <mach-o/dyld.h>
+#endif
 
 #include "dynloader.h"
 
 
-static NSObjectFileImageReturnCode cofiff_result = NSObjectFileImageFailure;
+#ifdef HAVE_DLOPEN
+
+void *
+pg_dlopen(char *filename)
+{
+	return dlopen(filename, RTLD_NOW | RTLD_GLOBAL);
+}
+
+void
+pg_dlclose(void *handle)
+{
+	dlclose(handle);
+}
+
+PGFunction
+pg_dlsym(void *handle, char *funcname)
+{
+	/* Do not prepend an underscore: see dlopen(3) */
+	return dlsym(handle, funcname);
+}
 
+char *
+pg_dlerror(void)
+{
+	return dlerror();
+}
+
+#else /* !HAVE_DLOPEN */
+
+/*
+ * These routines were taken from the Apache source, but were made
+ * available with a PostgreSQL-compatible license.	Kudos Wilfredo
+ * Snchez <wsanchez@apple.com>.
+ */
+
+static NSObjectFileImageReturnCode cofiff_result = NSObjectFileImageFailure;
 
 void *
 pg_dlopen(char *filename)
@@ -92,3 +131,5 @@ pg_dlerror(void)
 
 	return (char *) errorString;
 }
+
+#endif /* HAVE_DLOPEN */