Update lua-ev for Lua 5.2

Hi!  I've been trying to get familiar with libev and libevent through Lua.  I really love what you've written here and I thought I could help by updating it for 5.2!

What Changed:
1) invalid type: luaL_reg -> luaL_Reg
2) luaL_register() has become luaL_setfuncs() & luaL_newlib() respectively
3) getfenv()/setfenv() on userdata became getuservalue()/setuservalue()
4) luaL_typerror() became a private function in 5.2 (upstream-Lua sucks sometimes)
5) dumper.lua was unnecessarily escaping ] which 5.2 didn't like (5.1 did not care)
6) added a FindLua52.cmake for figuring out where liblua.so is
7) made a macro for quicker "constant pushing" in lua_ev.c & alphabetized said constants

I tested building this for Lua 5.1 and 5.2, everything cleared -- all the tests succeeded.  If you want to build for 5.1 again you change the 52 in CMakeLists.txt to 51 and all is happy in the Land of Lua.  Hope you'll accept this :-)