smb_msghashes() now takes a "BOOL dupechk" argument, if false, text hash

is "marked" to be ignored (by smb_findhash) when searching for dupes.
smb_addhashes() now takes a "BOOL skip_marked" argument, if false, all hashes
are written (even if marked).
These changes were necessary to have smb_addmsg() always store the hash of
the message text, but only compare for dupes if "dupechk" is TRUE. This allows
a sysop to later enable dupe checking and still detect dupes of older messages.