py3: catch FileExistsError instead of checking errno == EEXIST

py3: catch BrokenPipeError instead of checking errno == EPIPE

py3: catch ChildProcessError instead of checking errno == ECHILD

py3: remove retry on EINTR errno Since the implementation of PEP 475 (Python 3.5), Python retries system calls failing with EINTR. Therefore we don’t need the logic that retries it in Python code.

py3: stop catching TypeError that was raised on Python 2

py3: use `x.hex()` instead of `pycompat.sysstr(node.hex(x))`

tests: assume that `raw` attribute is present on original socket file object It seems like the original socket file object is always an io.BufferedIO instance. If not, the code will fail and we should try harder to get the socket object (e.g. if the original socket file object is unbuffered, we can get the `_sock` attribute directly from it).

tests: constant-fold a `pycompat.ispy3` in testlib/badserverext.py

tests: remove Python 2 special cases in test-stdio.py

py3: remove dead code to make file descriptors non-inheritable On Python 3, file descriptors are already non-inheritable by default.