Print a warning in the case that we remain bound
to an old essid even though we asked for a newer one.
I'm still not clear how that can happen.
Fix a bug with persistent schemes:
After accepting a new scheme and saving it successfully,
sometimes, inexplicably, it loops back:
Save this scheme for later? (y/N) y
Trying to write scheme to /home/akkana/.config/netscheme/.netscheme
Use it anyway? (Y/n)

I think this was happening when there were two schemes both matching
the current essid, because we didn't break out of the loop.

Also, if persistent is specified then we shouldn't ask "save this scheme
for later?" anyway -- obviously we need to save a persistent scheme.
Break out of the loop over known schemes
when we find a scheme matching the one specified.
Fixes a bug where the wrong scheme would be saved to the current file.