upstream: when checking that filenames sent by the server side

match what the client requested, be prepared to handle shell-style brace
alternations, e.g. "{foo,bar}".

"looks good to me" millert@ + in snaps for the last week courtesy
deraadt@

OpenBSD-Commit-ID: 3b1ce7639b0b25b2248e3a30f561a548f6815f3e

Discussed with:	des