- split_whitespace(): slightly better memory ref handling when errors
  occur.

- strop_joinfields(): First argument can now be any sequence-protocol
  conformant object.

- strop_find(), strop_rfind(): Use PyArg_ParseTuple for optional
  arguments

- strop_lower(), strop_upper(): Factor logic into a common function
  do_casechange().

- strop_atoi(), strop_atol(): Use PyArg_ParseTuple.

- strop_maketrans(): arguments used to be optional, although the
  documentation doesn't reflect this.  Make the source conform to the
  docs.  Arguments are required, but two empty strings will return the
  identity translation table.

- General pass fixing up formatting, and checking for return values.