Tkinter converts str argument to C string and then pass it to Tcl. But Tcl handles string length as int and it can overflow if strlen() returns value > INT_MAX. Proposed patch introduces special conversion functions which ensure that string length will not overflow. It also corrects error message in getint(), getdouble() and getboolean() methods (e.g. "must be int or str" instead of "must be str") and adds tests for them.
Here is a little simpler patch. Instead of checking string length in custom converter, it is checked after invocation of PyArg_ParseTuple. Also added bigmem tests.
