Update the user guide.

1) Backport `path_find`
2) Disable debuginfo in RPM
3) Disable failing part of BSDSocket test

+ fix socket:readline regexp.

+ fix bsdsocket test

 * Move source files to appropriate location
 * Remove C wrapper for isysconnect/sysbind/sendto and
 * other functions
 * Remove box.socket.errno()
 * Change sockets to be non-blocked by
 * default
 * Code style fixes
 * Other minor changes

 + memory leak in box.net.box (timeouted responses)
 + remote:ping() never throw exception

Closes #161

move module related tests from test/box/ to test/module/.

Summary:
* PLUGIN_DIR -> MODULE_DIR
* MODULE_DIR prefix is /usr/lib/tarantool/VERSION
* MODULE_DIR automatically appends to both lua c/path
* removed plugin autoload facility in src/lua/init.cc
* removed admin console plugin dependencies
* moved src/box/lua/sql.lua to separate module = require('box.net.sql')
* moved src/plugin/pg = require('box.net.pg')
* moved src/plugin/mysql = require('box.net.mysql')
* default .so and .lua install is lib/tarantool/modules/{box/net/}
* debian spec and tests are updated

Rationale:
Any error which implies a system administrator action needs to be
marked explicitly in the log, so that it's easy to find and act
upon.

This change the number of log levels, so the default log level was
bumped from 4 to 5. Installations which set the log level
explicitly need to adjust their setting.

+ use luaL_ref/luaL_unref to store lua scalar instead lua metatable.
+ add :is_closed method.

fixes, follows from discussion https://github.com/tarantool/tarantool/issues/79#issuecomment-29309533

This patch implements show index and shows memory waste of the
slab allocator.

A dead fiber could get reused prematurely or garbage collected twice.

This was because __gc could get invoked way after the fiber has
finished and reused for a different coroutine.

The fix is to always access fibers in Lua by fiber id.

Fix a hang on box.fiber.resume() of an attached fiber which gets
cancelled.
When the child fiber got cancelled before detach, the parent
never was woken up, and would hang forever.
Wake up the parent, and, in the parent, do not try to access
a dead fiber.

This patch limits maximum recursion depth for luaL_packsize and luaL_packvalue
functions to 16 nested tables. This check is needed to prevent a crash
on recursive Lua tables.