Builtin function 'length' properties

[toshok]

The builtin functions provided in the environment have 'length' properties spelled out in ecma262. we should do a pass over all methods and use new macro EJS_INSTALL_ATOM_FUNCTION_LEN_FLAGS (check in ejs-array.c or ejs-string.c for usage) everywhere. then likely change the macro's name and get rid of the other macros.