Actually fix the bug and add a test case.

closes gh-1428

+ closes gh-1405 (right path for unix socket)
+ wrap box.cfg and loadfile with pcall
+ some variable/function scope cleanups (global -> local)
+ closes gh-1409 (check for lua syntax before running/restarting/eval server)

Ensure that every box operation can take tuple as key/tupl/operation in
both engines

* Set version to {1, 6, 8} in box.space._schema
* Add 'LUA' language to built-in stored procedures

Use box.schema.upgrade() to upgrade.

./extra/schema_fill.lua and ./extra/schema_erase.lua were
moved to box.internal.bootstrap().

 * extra arguments silently ignored
 * :get and :put interpret nil timeout as infinity

Implement space:count() as a counterpart to space:len() for consistency
with space.index.

The new tarantool-python driver returns tuple from space
operations.

Implement box.cfg { read_only = true }

bool is_ro is now controlled by box.cfg{} and is not used by
register/unregister logic in _cluster table.

See #1349

Tarantool doesn't have CREATE, DROP or GRANT OPTION privileges.
Thus grants on an object can only be given by the creator (definer,
owner) of the object or admin.

The error message about this was misleading.

* Never ever ever raise "tuple is not array" from CALL
* Support ALL use-cases from #291 (Seriously!)
* Add test cases for #1167
* Remove buggy luaL_isarray()
* Extract tuple_to_mpstream()
* Optimize luamp_encode_tuple() to use tuple_to_mpstream()
* Other performance optimizations

This code shouldn't introduce perfomance regression because
it still does the same number of operations for all use cases.

* Convert to TAP
* Add gh ticket numbers for all test cases
* Get rid of global variables