Little refactoring +xlog, +snap, snapshot->snap

Be more verbose when exiting the spawner.

When tree.max_size is 0, tree.max_size * 2 is also 0.

lua print(io.popen("ls -la /root/;uname -a;"):read("*a"))

is not nice.

n  - big endian int16
N  - big endian int32
qQ - big endian int64
f  - float
d  - double

Using box.socket:recvfrom on udp socket causing 100% CPU
utilization instead of idle
https://bugs.launchpad.net/tarantool/+bug/1209189

@todo: manage instances in /etc/tarantool

Thanks for Anatol Pomozov

Hat tip to Alexey Panfilov

Make w3c isopub.ent entity files available locally,
since it is part of nobody-knows which package on Ubuntu,
and may be missing completely on other distributions.

On Ubuntu 13 even though it is part of mathml, it's not listed
properly in /etc/xml/catalog apparently.

This fixes xsltproc warnings and speeds up manual generation
significantly.