procutil: introduce context-manager interface for protect/restorestdio The code looks slightly cleaner since it was pretty easy to pass arguments in wrong order.

procutil: move protectio/restoreio from commandserver Some variants of this will be useful for stdio-based servers such as sshserver.

commandserver: rewrite protectio/restoreio to not depend on ui Prepares for porting to utils.procutil, in which ui shouldn't be known. ui.flush() is replaced with ui.fout.flush() since ui.ferr wasn't involved.

util: deprecate procutil proxy functions (API) Several functions are re-exported by utils.procutil, which require explicit modname parameter. .. api:: Utility functions related to process/executable management have been moved to utils.procutil module.

procutil: bulk-replace function calls to point to new module

procutil: bulk-replace util.std* to point to new module

procutil: move process/executable management functions to new module std* files, pipe helpers, and findexe()s are moved as well since they are likely to be used with sub processes.

util: stop using readfile() in tempfilter() To unblock code move to utils.*. It's merely two lines of very Pythonic code. No helper function should be needed.

util: mark filtertable as private constant Prepares for porting to utils.*.

util: mark platform-specific gethgcmd() as private util.hgcmd() is the public interface for gethgcmd().

test-pathconflicts-merge: stop requiring symlink support The errors from the last time I took a shot at this back in early November have disappeared, so let's just enable this.

commands: use constants for merge things We have nice constants now. Let's use them to make the code easier to reason about. Differential Revision: https://phab.mercurial-scm.org/D2702