I've decided that trying to do wildcards in PSFTP as a special case
of directory recursion was a strategic error: it obfuscates
sftp_{get,put}_file(), and also it makes it very hard to handle
subdirectory wildcards such as `foo/*'. Accordingly, here's a
completely different approach, in which sftp_{get,put}_file() are
still responsible for directory recursion, but wildcards are
expanded in sftp_general_{get,put}() before being passed thereto.
Subdirectory wildcards are now handled consistently across Unix,
Windows and the remote server.