gh-983 still needs a test case.

In case of partial write the savepoint was advanced beyond end position.

With structured configuration, i.e. a Lua table for a list of
replication peers, it is difficult to pass a configuration option
to the hook function as a single C object. Don't pass
options in, but query them from the hook function with cfg_get*
API.

As a result, all "change" hooks have the same signature now,
a step closer to the pluggable configuration API.

Introduce a layer of wrappers for a number of internal box functions,
dealing with accss to spaces and indexes.

These wrappers:
    * don't throw exceptions
    * have a common prefix box_
    * are exported in the server development headers

Rewrite Lua C bindings to use the public API described above.
Rewrite Lua FFI bindings to do the same.
Add test.

- update comments
- fix the logic of partial write recovery (still needs a test)

Conflicts:
	src/box/alter.cc
	test/app/snapshot.test.lua

* style fixes
* fix a bug in key opts decoder (alter.cc)
* ensure dimension is visible in box.space
* rebuild bootstrap.snap to use the new format

cmake 2.8.9 doesn't have CMAKE_CXX_COMPILER_VERSION

- fix net.box to satisfy strict.lua requirements
- after review fixes
- fix buffer:checksize() in buffer.lua

When entire contents of the output buffer is flushed, we must reset
write start and end positions. If the buffer can be recyced, they
both are reset to point to the beginning of the buffer, otherwise write start
is advanced to match write end.

The old code would always execute *begin = *end assignment, regardless
of whether it's case 1) (full reset) or 2) (advancing write start).

gcc 4.8 could reorder this assignment, and put it in front of conditional
iobuf_reset(). In that case, write start could point beyond write end,
since iobuf_reset() resets write end to zero.

A funny bug which would hit only under heavy load, only if there are
-O2 optimizations, and no debug prints.