notmuch-insert Fcc handling w/spaces in dir name

[Keith Amidon]

I just upgraded to 0.23 and tried out the Fcc handling using notmuch-
insert.  I think this is a significant improvement and I'm excited to
use it.   I have it working successfully for my use case now, but it
did require one workaround that I didn't expect and that seems somewhat
fragile.

The issue is that I'm synchronizing with Gmail and I'd like my sent
mail to be synchronized too.  Therefore I have to insert into the
directory Gmail expects, which is "[Gmail]/Sent Mail".  Notice the
space in the directory name.

I was able to make this work by setting notmuch-fcc-dirs to:

   "\"[Gmail]/Sent Mail\" +sent -inbox -unread"

This works because the Fcc handling constructs a shell command to run
by just appending the notmuch-fcc-dirs value to (in the simple case)
"notmuch-insert --folder=", so the extra double quotes in my notmuch-
fcc-dirs value quote things appropriately at the shell level.

While this works, depending on passing through shell quoting seems very
fragile.  Changes in the implementation could break this solution
without it being obvious why.  It seems like it would be better if the
notmuch-fcc-dirs value could be something like:

    ("[Gmail]/Sent Mail" "+sent" "-inbox" "-unread")

Then the code could generate the shell command with appropriate
quoting.  I took a quick look at implementing this but it looked more
complicated then I had time to invested right now.  I thought it would
be good to get the issue out for discussion ASAP since this new
functionality was just released.

      Cheers!   Keith