Fix bug
https://bugs.launchpad.net/tarantool/+bug/983094
"Valgrind tests were broken by WAL writer patch"

Keep track of WAL files opened for write
in recovery

Extend atfork handler to clear the wals,
to avoid collision with reuse of recovery
to save a snapshot.

Move some WAL-specific configuration settings
from wal_class to recovery, to avoid layers
of indirection when doing RELOAD CONFIGURATION

Conflicts:
	mod/box/box.lua
	test/box/lua.result
	test/box/lua.test

tarantool_lua_dofile function was rewritten.

Fix brokken static compilation of the client (we'll have
to find another solution for Darwin).

Review changes:
  * tarantool_lua_load_startup was renamed to tarantool_lua_load_init_script;
  * TARANTOOL_LUA_STARTUP was renamed to TARANTOOL_LUA_INIT_SCRIPT;
  * init.lua int the test suite is optional now;
  * Additional comments was added.

Fix bug https://bugs.launchpad.net/tarantool/+bug/988701
"Build with '-DENABLE_CLIENT=true' was broken'

Until
https://bugs.launchpad.net/tarantool/+bug/962848
"Compilation with extrnal LuaJIT broke with addition of FFI"
is fixed, don't try to compile with external LuaJIT.

Update the manual and the configuration file
to reflect the new WAL writer architecture.