Fix #72: print() in background fiber hogs fiber gc memory pool
Merge branch 'gh-72-print-palloc-memleak' into stable
Replace luaL_Buffer with tbuf. Fix #65
Fix #123: box.index.count and box.index.iterator do not check arguments

This patch adds lua_checkfield function - a wrapper for lua_tofield that raises
an error if Lua type can not be converted to lua_field structure. The function
should be used instead of lua_tofield in all bindings where custom types are not
supported.
Fix #122: box.pack('p', t) segfault on recursive tables

This patch limits maximum recursion depth for luaL_packsize and luaL_packvalue
functions to 16 nested tables. This check is needed to prevent a crash
on recursive Lua tables.
Merge branch 'gh-123-box-count-arg-check' into stable
A fix and a test case for gh-131

Fix a hang on box.fiber.resume() of an attached fiber which gets
cancelled.
When the child fiber got cancelled before detach, the parent
never was woken up, and would hang forever.
Wake up the parent, and, in the parent, do not try to access
a dead fiber.
Merge remote-tracking branch 'origin/stable' into fiber-problem

Conflicts:
	test/box/lua.result
minor tweaks.