Fix #346: yaml.null() crases server

This patch also adds NULL constant to yaml, msgpack, msgpackffi
and json serializers.
- Create 3 new rpm-specs:
  * extra/rpm/tarantool-scl.rpm.spec - SCL spec for 1.5
  * extra/rpm/tarantool-el.rpm.spec.in - Enetrprise Linux 5/6 Specification
  * extra/rpm/tarantool.rpm.spec.in - Specification for other Linuxs
- Build (tarantool-el.rpm.spec and tarantool.rpm.spec) with `--define 'scl 15'`for SCL build.
- Preserve old spec (for compatibility)
- Add dependencies into Specifications, two specs for Mock.
- Create configuration files for Mock builds for EL-{5,6}-{i386,x86_64}

  Working with Mock:
    cmake .
    make new_rpm{_el,}_src
    mock -r <config> --init
    mock -r <config> --rebuild <path_to_srpm>

  Merging commits
Update rpmspec
* Move building of modules into Lua (in rpmspec)
* Remove tarantool.cfg and init.d/tarantool_box from SCL spec (bug in cmake28-epel-6-x86_64)
* Merge two specs (for EL and other RPM linuxes)
* Add Fedora's Mock specifications
Merge branch 'stable'

Conflicts:
	.gitignore
	extra/CMakeLists.txt
	test/CMakeLists.txt
Fix errors in rpm.spec.in when merging with stable.
Fix error related to absence of rpmbuild
Merge branch 'stable'
Add generating src.rpm in the current dir
Merge branch 'stable'
Merge branch 'master' of https://github.com/tarantool/tarantool