Split dirvish-yank--execute into two functions

[dvzubarev]

It could be useful for overriding the code that creates external process for actual yank operations (rsync or copy/move).
For example, I override new method (dirvish-yank--start-proc) in my fork of detached.el library.
It allows me to detach execution of rsync command from the Emacs instance. Also detached.el provides better monitoring and alerting facilities.

[alexluigit]

Thanks @dvzubarev! I'm wondering why would you care about detaching the yank process, I personally find yank (not rsync) command can be really slow when calling on remote connections, but the speed is OK when running locally.

[dvzubarev]

Sometimes I run rsync on large files (tens or hundreds of GiB). It takes some
time to finish.

I've started using detached.el recently for launching long-running scripts and
I've setup failure/completion notifications on my phone and desktop. So I thought I
could use it for long running rsync processes. Also I could easily kill
long-running rsync from Emacs when it is detached. I do not need this feature
often, but once or two I had to go down to command line to track rsync process
that I mistakenly started and kill them. All of this (notification, process
termination) could be implemented in dirvish, but as I said I started using
detached.el for other purposes and wanted to quickly adapt dirvish for it.