The 'which' command is an external command that must be called each and
every time pass is used. 'which' is also not mentioned in the README as
one of the dependencies that might be needed to run pass.

Instead of 'which', we can use the POSIX compatible and shell built-in
'command -v'. It saves pass from making an external call and is,
arguably, more reliable than using 'which' as mentioned in the following
link.

"brew --prefix gnu-getopt" takes 2.125s on my very default setup (I
don't even want to know why), dominating the pass wall time.

If the default brew prefix is in use, just detect the getopt binary with
a cheap "test -x" instead.

This doesn't detect if XQuartz is installed and running, so it's broken
in most setups, the experience is poor regardless, since it's not
displayed inline in the terminal, but leaves a window that requires
closing, and anyway the the utf8 mode works perfectly on both iTerm2 and
Terminal.app.

Instead we're forced to base64 it, like we do with the clipboard.

While we do not expect any output on stdout from the background task,
keeping the file handle open means that anyone calling `pass` and
waiting for stdout to be closed, will have to wait (by default) for 45
seconds.