Replace metaperf gedents code with a more useful readdir operation; add some auto-bench scripts for metaperf runs; fix a divide-by-zero in dirperf

run.metaperf_10i_1000n

@@ -0,0 +1,14 @@
+#!/bin/sh
+# 
+# Runs the metaperf metadata micro-benchmark.
+# Use 1000 files, 10 iterations.
+# 
+
+. $here/common.metaperf
+
+if [ $# -gt 0 ]; then
+    _format_header
+    exit 0
+fi
+
+$here/src/metaperf -d . -i 10 -n 1000 -l15 $allops | _format_metaperf