common: add missing CDECL-wrapper to debug-info.h.
common: don't include unused syslog.h in log.h.
lua-5.2: provide lua_objlen compatibility macro if necessary.

If Lua is compiled without LUA_COMPAT_ALL luaconf.h will not
provide a few macros for backward-compatibility, including
lua_objlen. Detect this and provide lua_objlen in lua-utils.h
if necessary.