coio: add *_noxc read / write functions

The popen implementation is written in C and uses coio read / write
functions. If an exception occurs, it'll pass through the C code. It
should be catched to proceed correctly.

We usually have foo() and foo_xc() (exception) functions when both
variants are necessary. Here I added non-conventional *_noxc() functions
as the temporary solution to postpone refactoring of the code and all
its usages.

Part of #4031

Acked-by: Cyrill Gorcunov <gorcunov@gmail.com>