third_party: Import code.google.com/p/go.crypto/scrypt.

Change-Id: I39a2e08749a68e0a1234d0488a592b8f43eec594
pkg/sorted/kvfile: add sorted.Wiper.

This allows people with kvIndexFile in their server-config.json to run:
camlistored -reindex

Change-Id: If1008297fa29ca514260529edb2125a1ea7d5246
Merge "pkg/sorted/kvfile: add sorted.Wiper."
Merge "third_party: Import code.google.com/p/go.crypto/scrypt."
sorted/kvfile: make it actually compile

Change-Id: I0a3916c1c260dfac6b3444a18510a013d429ef33