Use a vendor directory for repeatable builds - fixes #816

This is using godep to manage the vendor directory.

vendor/bazil.org/fuse/unmount.go

@@ -0,0 +1,6 @@
+package fuse
+
+// Unmount tries to unmount the filesystem mounted at dir.
+func Unmount(dir string) error {
+	return unmount(dir)
+}