Fix #566, where __getslice__ generates code that gives a confusing compiler error under Python 3.  (Now you get a Cython compiler warning and a direct error message.)  A modification of the patch for #215.

trac #561: fixed major performance bug in special functions (by not generating Python versions and letting PyType_Ready() do it instead; details are on the trac ticket)

temp_expression must free its temps as early as possible

code cleanup for function default arguments, make sure we keep any executable C code behind the type declarations in the function header regardless of how we get to the default values

fix performance hit in argument unpacking when passing keyword arguments into functions that have both required positional and optional keyword arguments