vsftpd security and bug fix update

[2.0.1-6]

• add option max_login_fails that kicks the session after few login fails
• Resolves: #197141
• fix bad handling of unique files
• Resolves: #250727
• increase maximum length of allowed username
• Resolves: #236326
• fix create/lock race condition when more clients are uploading to a file
• Resolves: #240550
• document lock_upload_files option
• Resolves: #316381
• allow usernames to begin with underscore or dot
• Resolves: #339911
• dont reply with code 150 two times when uploading files with STOU
• Resolves: #387021
• fix memory leak in ls.c
• Resolves: #408431
• daemonize correctly and report startup failure correctly
• Resolves: #206843
• fix init script
• Resolves: #431450