Central rsync backup server

Features:

RSYNC_PORT=6502 ./rsync-piper.pl
	- generate rsync configuration based on content of RSYNC_DIR/users
	- start rsync server on specified port
	- follow rsync transfer log, parse it and trigger events
	- file/dir metadata in json (with VFS-like API)
	- deduplicate files using md5 pool and hardlinks
	- gearman log shipping in json format
	- support login+host usernames for client secrets
	- push md5sum file to create files from server's md5 pool

data-worker.pl
	- gearman worker to store rsync transfer log into PostgreSQL

create-user.sh
remove-user.sh
	- create/remove user's directory and data

test.sh
	- excercise rsync server to test basic operation and deduplication


Installation on Debian:

$ ./bin/debian-install.sh

Disk quota calculation depends on custom POSIX ids created using libnss-extrausers
so ensure that /etc/nsswitch.conf has extrausers enabled:

$ egrep '^(passwd|group):' /etc/nsswitch.conf 
passwd:         compat extrausers
group:          compat extrausers

Install default test user and first slice:

$ sudo cp -v extrausers/* /var/lib/extrausers/
`extrausers/group' -> `/var/lib/extrausers/group'
`extrausers/passwd' -> `/var/lib/extrausers/passwd'