fdtrack: temporary hack for tracking file descriptor usage

Package fdtrack logs statistics about open file descriptors.
This should help identify the source of #1549.

fdtrack/fdusage.go

@@ -0,0 +1,29 @@
+// Copyright 2015 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// +build !linux,!darwin
+
+package fdtrack
+
+import "errors"
+
+func fdlimit() int {
+	return 0
+}
+
+func fdusage() (int, error) {
+	return 0, errors.New("not implemented")
+}