Use check_symbol_exists(), not check_function_exists(),
to discover fdatasync(), since apparently on some BSD systems
the symbol is present in the library but not in the headers
(I hope not vice versa).

Don't use check_prototype_definition, since it's not available
in CMake 2.6.

 * sys/prctl.h can be found only on Linux, but cmake recognizes Debian/kFreeBSD
 as Linux.
 * extern "C" for TIMEOUT_INFINITY (it is used in plugins)

Rename tarantool_pthread.h to tt_pthread.h

This is a pre-requisite for addition of Perl stored procedures.

g++ (not gcc) works correctly when dealing with
extern __inline and __extern_inline constructions, thus
this hack is not necessary now.

The patch which removes the CPack-generated spec
and adds a proper spec for client, server and library
was done by Dmitry Simonenko.

Hand-port the patch to the master, since it's gone too
far away from the origin and merging it ends up in a mess.

Code review of cjson branch by Dmitry E. Oboukhov.
Hand-picking the changes since the original branch
is based on import of lua-cjson into Tarantool
revision tree, and this branch is based on a git
submodule.

This patch implements
https://blueprints.launchpad.net/tarantool/+spec/lua-cjson

This patch needs for correct work of out-of-source builds
from tarbals without .git repository within.

autogenerate version file which can be used
in case when there is no .git repository available within sources and
it is crucial to properly display current version.

Don't pollute test/unit include space with
third_party includes.