This avoids possible buffer overreads when int(), float(), compile(), exec()
and eval() are passed bytes-like objects. Similar code is removed from the
complex() constructor, where it was not reachable.

Patch by John Leitch, Serhiy Storchaka and Martin Panter.

This changes the main documentation, doc strings, source code comments, and a
couple error messages in the test suite. In some cases the word was removed
or edited some other way to fix the grammar.

Also factored out some test cases into a new PtyTests class.