[9fans] allowing space (ASCII 0x20) in file names

[Russ Cox rsc@plan9.bell-labs.com]

> The problem is that the RFC2060 "International Mailbox Naming
> Convention" has one more character in its alphabet than Plan9
> allows in names so there is no place to map the space.

There are more problems than that.  I'm pretty sure RFC2060 doesn't
specify a name length, and Plan9 limits you to 27 bytes.  So you're
going to have to keep some sort of translation table between IMAP
names and Plan9 names anyway.  

If this limit wasn't there and you were content to keep the mailbox
names in encoded form (probably a nice choice, since then you never
have to decode or encode them) you could substitute 0x7F for space
in the Plan9 names and you'd be all set -- both are one byte in
UTF-8, and RFC2060 can't have raw 7Fs while Plan9 can't have raw spaces.

Russ