This will hopefully get rid of some Coverity warnings, be a hint to
developers, and be marginally faster.
Some asserts were added when the type is currently known, but depends
on values from another function.
In C++, it's an error to pass a string literal to a char* function
without a const_cast(). Rather than require every C++ extension
module to put a cast around string literals, fix the API to state the
const-ness.
I focused on parts of the API where people usually pass literals:
PyArg_ParseTuple() and friends, Py_BuildValue(), PyMethodDef, the type
slots, etc. Predictably, there were a large set of functions that
needed to be fixed as a result of these changes. The most pervasive
change was to make the keyword args list passed to
PyArg_ParseTupleAndKewords() to be a const char *kwlist[].
One cast was required as a result of the changes: A type object
mallocs the memory for its tp_doc slot and later frees it.
PyTypeObject says that tp_doc is const char *; but if the type was
created by type_new(), we know it is safe to cast to char *.
[ 1327110 ] wrong TypeError traceback in generator expressions
by removing the code that can stomp on the users' TypeError raised by the
iterable argument to ''.join() -- PySequence_Fast (now?) gives a perfectly
reasonable message itself. Also, a couple of tests.
