This adds support for gitignore-like wildcards and exclude patters in
reverse mode. It (somewhat) fixes#273: no regexp support, but the
syntax should be powerful enough to satisfy most needs.
Also, since adding a lot of --exclude options can be tedious, it adds
the --exclude-from option to read patterns from a file (or files).
Give the gocryptfs process one extra millisecond to close
files. Allows us to drop several other sleeps.
UnmountErr now really returns an error when it detects an fd leak
instead of just printing a message.
