read or readall methods no longer lose data when an underlying read
system call is interrupted within an io module object. IOError is no
longer raised due to a read system call returning EINTR from within
these methods.
This is a backport of changeset 781b95159954 from 3.2.
The earlier 2.7 changeset 67dc99a989cd already fixed this for the
builtin python 2.x file object.
This is for consistency with imitation file objects like StringIO and BytesIO.
This commit also adds a few tests, where they were lacking for concerned
methods.
Gregory P. Smith
Antoine Pitrou
Benjamin Peterson
Mark Dickinson