#8271: the utf-8 decoder now outputs the correct number of U+FFFD  characters when used with the "replace" error handler on invalid utf-8 sequences.  Patch by Serhiy Storchaka, tests by Ezio Melotti.

Previously, excessive nesting in expressions would blow the
stack and segfault the interpreter. Now, a hard limit based
on the configured recursion limit and a hardcoded scaling
factor is applied.

Patch by Alessandro Moura.

Patch by Guillaume Pratte.