Projects/Replay cache improvements

This is an early stage project for MIT Kerberos. It is being fleshed out by its proponents. Feel free to help flesh out the details of this project. After the project is ready, it will be presented for review and approval.

http://colabti.org/irclogger/irclogger_log/krbdev?date=2014-08-26

Existing race condition when creating (or replacing on corruption). [krbdev.mit.edu #3498]

Possible file corruption due to lack of locking and not using O_APPEND [krbdev.mit.edu #1671]. Probable mechanism is two processes nearly simultaneously writing at the same file offset, which will cause overlapping writes unless O_APPEND is set.

Use of fsync() can cause performance problems. [krbdev.mit.edu #372]