bug#18940: 24.4; vc-hg does not disable pager, leading to hangs (at least with tramp)

[Stefan Monnier]

> Maybe I'm missing something, but what's wrong with let-binding
> process-environment?

Nothing wrong with it.  The problem is that Tramp ignores those
let-bindings because it fails to propagate this environment to its
remote sub-processed.

`tramp-sh-handle-process-file' really needs to compare
process-environment with (default-toplevel-value 'process-environment)
to infer the env-vars that have been added via let-binding and then
propagate those to the remote sub-process.


        Stefan