[issue36865] FileInput does not allow 'rt' mode, but all its existing delegates do

[SilentGhost]

Change by SilentGhost <ghost.adh at runbox.com>:


----------
nosy: +berker.peksag
versions:  -Python 3.5, Python 3.6, Python 3.7

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36865>
_______________________________________