While we're at, using the slightly more portable `command -v` technique
to detect the executable. Also, there's no need to use `io.popen()` if
we aren't going to record the path. Instead, let's use the simpler
`os.execute()` to detect the presence of xclip.
The vim_input function accepts raw terminal input and so is better to emulate
real user, especially because it is not deferred as vim_feedkeys.
Using this function required a number of changes:
- expect() was refactored to use curbuf_contents()
- The vim_eval function in request() was moved to curbuf_contents(). For most
cases this is enough(we only care for synchronizing api calls with user input
when verifying buffer contents).
- <C-@>(NUL) is preprocessed before being passed to replace_termcodes.
- Legacy test 4 had a bug that only became visible when using vim_input, it is
fixed now.
- An extra blank line deletion was required for test 101
The last two items show that vim_feedkeys because it is not 100% equivalent to
receiving terminal input.
Commit @45525853d352 removed usage of the `job_write_cb` for closing stdin due
to a memory error, but that doesn't work anymore because `job_close_in` closes
stdin immediately, possibly trimming input data before it is fully written.
Since most memory issues with jobs have been fixed, re-add the `job_write_cb`
call to ensure stdin is only closed when it should. Also add tests for scenarios
where using the callback makes a difference.
It's possible that a child process won't close it's standard streams, even after
it exits. This can be evidenced with the "xclip" program:
:call system('xclip -i -selection clipboard', 'DATA')
Before this commit, the above command wouldn't return, even though the xclip
program had exited. That is because `xclip` wasn't closing it's stdout/stderr
streams, which would block pending_refs from ever reaching 0.
Now the job.c module was refactored to ensure all streams are closed when the
uv_process_t handle is closed.
