real-time signals.

 * Ensure that the input string is ready
 * Raise a ValueError instead of of a fatal error

PyUnicode_WriteChar() raises also a ValueError if the string has more than 1
reference.

unicode_getitem() reuses PyUnicode_ReadChar()

Patch by Dan Kenigsberg.

Issue #13034: When decoding some SSL certificates, the subjectAltName extension could be unreported.

Issue #13034: When decoding some SSL certificates, the subjectAltName extension could be unreported.

Rewrite unicode_subtype_new(): allocate directly the right type.

 * Rename existing _PyUnicode_UTF8() macro to PyUnicode_UTF8()
 * Rename existing _PyUnicode_UTF8_LENGTH() macro to PyUnicode_UTF8_LENGTH()
 * PyUnicode_UTF8() and PyUnicode_UTF8_LENGTH() are more strict

Issue #12804: Prevent "make test" from using network resources.

Fix also a bug: call PyUnicode_READY() before reading string length.

These were just an artifact of the old unicode concatenation hack and likely
just penalized other kinds of adding. Also, this fixes __(i)add__ on string
subclasses.

 * Optimize unicode_repeat() for a special case with memset()
 * Simplify integer overflow checking; remove the second check because
   PyUnicode_New() already does it and uses a smaller limit (Py_ssize_t vs
   size_t)

 * PyUnicode_Substring() now fails if start or end is invalid
 * PyUnicode_Substring() reuses PyUnicode_Copy() for non-exact strings

 * PyUnicode_Copy() is faster than substring()
 * Fix also a compiler warning