Attaching of a socket to existing channel

It's possible first create a channel and write to it and then attach socket.
Merge pull request #37 from andrusha97/master

Attaching of a socket to existing channel
Merge branch 'master' of github.com:cocaine/cocaine-core
Log wording and various eye-candy.
Be more verbose about bootstrap errors.

Instead of simply propagating service initialization errors to the
runtime, try to catch them and dump to the log first.
Fixed some missed code formatting issues.
Plugin preconditions support.

Blindly loading all the plugins sometimes led to SIGSEGVs and other
nasty stuff due to ABI incompatibilities and such. All the new versions
of all plugins should include a 'validation' symbol specifying plugin's
load preconditions from now on.
Unindent anonymous namespaces.
Expose plugin precondition check as a function.

I haven't managed to properly export the preconditions_t symbol from a
plugin, so instead of this it's now a function returning preconditions.
A bit more descriptive comment on Locator port.
Break the infinite loop in slave_t::pump().

If there are more sessions already assigned on a slave than allowed by
the profile, and still some sessions in the named queue, then pump will
enter an infinite loop.
Changelog bump - 0.10.5-14.