in pbs recipe.

This allow to update pbs section each time new slave instance
is added.

This try to swallow as much as possible slave instance bad requests.

I updated the dropbear url because it wasn't uploaded to network cache.
I kept an old version because :
 * our patches don't work anymore with the latest version.
 * the latest version (at the date of this commit, doesn't have an
   interesting changelog).
 * by laziness.

Boa is a single-tasking HTTP server. That means that unlike traditional
web servers, it does not fork for each incoming connection, nor does it
fork many copies of itself to handle multiple connections. It internally
multiplexes all of the ongoing HTTP connections, and forks only for CGI
programs (which must be separate processes). Preliminary tests show boa
is capable of handling several hundred hits per second on a 100 MHz
Pentium.

Description from : <http://packages.debian.org/squeeze/boa>
Building method inspired by :
<http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/www-servers/boa/boa-0.94.14_rc21.ebuild?view=markup>

Using a graceful restart :
<http://httpd.apache.org/docs/2.2/stopping.html#graceful>