Delete src/or/buffers.c which was fixup'ed in 0.2.9 but moved in 0.3.5.
The 0.2.9 fix is not required for the 0.3.5 patch.
Resolves merge conflict caused by 30041.

Fixes bug 31374; bugfix on 0.2.9.1-alpha.

My previous fix removed a comparison, which would have caused us to
warn about every skew instead of skews of over an hour.

Merge changed chutney and stem script lines from 29280 with changed
stem script lines from 30591.

Merge rust additions in 0.3.5 with sudo deletions in 0.2.9.

On some windows builds, time_t is 64 bits but long is not.  This is
causing appveyor builds to fail.

Also, one of our uses of labs() on time_t was logically incorrect:
it was telling us to accept NETINFO cells up to three minutes
_before_ the message they were responding to, which doesn't make
sense.

This patch adds a time_abs() function that we should eventually move
to intmath.h or something.  For now, though, it will make merges
easier to have it file-local in channeltls.c.

Fixes bug 31343; bugfix on 0.2.4.4-alpha.

And add some comments about stem

Part of 29280.