Use DEFFILEMODE (which is user/group/other read/writeable by default on *nix)

in smb_open*() when creating msgbase files.
smblib wasn't using the same default file creation mode (permissions) as
the rest of the Synchronet executables. smblib was creating msgbase files
as user read/writeable *only* (no group or other permissions) - so the umask
value for the group/other permissions flags had no effect on msgbase files
created via smblib.
This could lead to permissions issues for other users/groups on *nix systems
trying to access (read or write) msgbases. No change for non-*nix systems.

src/smblib/smbfile.c

@@ -156,7 +156,7 @@ int SMBCALL smb_open_fp(smb_t* smb, FILE** fp, int share)
 	SAFEPRINTF2(path,"%s.%s",smb->file,ext);
 
 	while(1) {
-		if((file=sopen(path,O_RDWR|O_CREAT|O_BINARY,share,S_IREAD|S_IWRITE))!=-1)
+		if((file=sopen(path,O_RDWR|O_CREAT|O_BINARY,share,DEFFILEMODE))!=-1)
 			break;
 		if(get_errno()!=EACCES && get_errno()!=EAGAIN) {
 			safe_snprintf(smb->last_error,sizeof(smb->last_error)