Refactor statement transaction lifecycle. Avoid nested
statement transactions. Make sure there is no more than 1
statement transaction present in the system at the moment.

Resolve the bugs this revealed:
- in local hot standby we would parasite on the main or
script fiber session to process requests. When an assert
was added that there is no more than 1 transaction active
at a given moment in time, it turned out that transactions
running on behalf of local hot standby were running in
the scope of session of the run_script or sched fibers.

Create and use an own session there.

- refactor session on_connect/on_disconnect trigger
invocation: do not invoke these triggers for just any session,
only for real connects/disconnects (iproto, admin).

- split session creation/destruction and trigger invocation
Conclude that session storage implementation needs to be
done differently.

Every fiber which may work with box needs to have a session,
since it's stores user id and the current transaction.

Conflicts:
	src/lua/bsdsocket.lua
	test/box/bsdsocket.result
	test/box/bsdsocket.test

This patch adds a new implementation of UUID library.
New library generates RFC4122 compatible random-based (version 4)
UUIDs using data from /dev/(u)random. The uuidgen(2) syscall is also
supported on BSD system. `struct tt_uuid` redefined from RFC4122.
Complimentary functions rewrotten to remove dependecy on e2fs libuuid.
Lua bindings refactored to use new library and support all features.

Closes #317

Fix Mac OS X Lion build by not adding -rdynamic by default.
Only use -rdynamic on Darwin (Konstantin Knizhnik's Mac).

Conflicts:
	src/box/lua/call.cc
	src/lua/init.cc
	test/box/net.box.result
	test/box/net.box.test.lua

Conflicts:
	doc/www-data.in/download.cmake