convert/mtn: add support for using monotone's "automate stdio" when available...
convert/mtn: add support for using monotone's "automate stdio" when available
Currently the convert extension spawns a new mtn process for each
operation. For a large repository, this ends up being hundreds of
thousands of processes. The following enables usage of monotone's
"automate stdio" functionality - documented at:
http://www.monotone.ca/docs/Automation.html#index-mtn-automate-stdio-188
The effect is that (after determining that a new enough mtn executable
is available) a single long-running mtn process is used for all the
operations, using stdin/stdout to send commands and read output.
This has a pretty significant effect on the performance of some parts
of the conversion process.
