Fixes for compilation issues

These changesets fixes 3 compilation issues:

1. Removed hard-coded CFLAGS and LDFLAGS and use pkg-config to generate the proper CFLAGS and LDFLAGS for lua. Previously, LDFLAGS included lualib which no longer exists since Lua 5.1. This causes linking against Lua 5.1 to fail. See: http://lua-users.org/lists/lua-l/2005-05/msg00186.html

2. Fixed unused variable warning in pythoninlua.c

3. Fixed incompatible pointer type warning in luainpython.c