Centralize implementation of delay code by creating a pg_usleep()

subroutine in src/port/pgsleep.c.  Remove platform dependencies from
miscadmin.h and put them in port.h where they belong.  Extend recent
vacuum cost-based-delay patch to apply to VACUUM FULL, ANALYZE, and
non-btree index vacuuming.

By the way, where is the documentation for the cost-based-delay patch?

src/port/pgsleep.c

@@ -0,0 +1,42 @@
+/*-------------------------------------------------------------------------
+ *
+ * pgsleep.c
+ *	   Portable delay handling.
+ *
+ *
+ * Portions Copyright (c) 1996-2003, PostgreSQL Global Development Group
+ *
+ * $PostgreSQL: pgsql/src/port/pgsleep.c,v 1.1 2004/02/10 03:42:45 tgl Exp $
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include <sys/time.h>
+
+
+/*
+ * pg_usleep --- delay the specified number of microseconds.
+ *
+ * NOTE: although the delay is specified in microseconds, the effective
+ * resolution is only 1/HZ, or 10 milliseconds, on most Unixen.  Expect
+ * the requested delay to be rounded up to the next resolution boundary.
+ *
+ * On machines where "long" is 32 bits, the maximum delay is ~2000 seconds.
+ */
+void
+pg_usleep(long microsec)
+{
+	if (microsec > 0)
+	{
+#ifndef WIN32
+		struct timeval delay;
+
+		delay.tv_sec = microsec / 1000000L;
+		delay.tv_usec = microsec % 1000000L;
+		(void) select(0, NULL, NULL, NULL, &delay);
+#else
+		SleepEx((microsec < 500 ? 1 : (microsec + 500) / 1000), TRUE);
+#endif
+	}
+}