Various changes "backportability"

[Michael Tokarev]

[Added some more active patch reviewers to Cc]

Hi!

Yesterday I wrote email about picking up changes from master
for previous stable release(s).  What's interesting is that
yesterday, basically in a single day, we've faced numerous
examples of subsystem changes which makes such backporting
significantly more difficult than might be.

For example, recent tpm bugfix, which is trivial by its own,
uses RETRY_ON_EINTR helper which were introduced recently and
which is now used everywhere.  coroutine_fn et al markers is
another example, translator_io_start is yet another, and so
on and so on.

When adding such subsystems/helpers which are to be used widely,
please split the initial implementation patch out of a single
"introduce foo; convert everything to use it" change.  Instead,
add the feature in a small patch first, and convert all users
tree-wide to it in a second, subsequent patch, maybe removing
the old version in that second patch too.  Where it makes sense
ofcourse, - sometimes it is not possible or just complicated to
do that, like when old and new implementations can't be supported
in parallel.

Just by splitting "introduce" from "convert", especially for
something simple which will be used all around, you'll greatly
simplify stable trees maintenance.

Thank you for consideration! :)

/mjt