cache drivers' ability to handle crlf in mails

it's a cheap call, but it clutters up log files.

src/sync.c

@@ -291,8 +291,8 @@ msg_fetched( int sts, void *aux )
 
 		vars->msg->flags = vars->data.flags = sanitize_flags( vars->data.flags, svars, t );
 
-		scr = (svars->drv[t^1]->get_caps( svars->ctx[t^1] ) / DRV_CRLF) & 1;
+		scr = svars->can_crlf[t^1];
-		tcr = (svars->drv[t]->get_caps( svars->ctx[t] ) / DRV_CRLF) & 1;
+		tcr = svars->can_crlf[t];
 		if (vars->srec || scr != tcr) {
 			if (!copy_msg_convert( scr, tcr, vars, t )) {
 				vars->cb( SYNC_NOGOOD, 0, vars );
@@ -475,6 +475,7 @@ sync_boxes( store_t *ctx[], const char * const names[], int present[], channel_c
 		}
 		svars->drv[t] = ctx[t]->driver;
 		svars->drv[t]->set_bad_callback( ctx[t], store_bad, AUX );
+		svars->can_crlf[t] = (svars->drv[t]->get_caps( svars->ctx[t] ) / DRV_CRLF) & 1;
 	}
 	/* Both boxes must be fully set up at this point, so that error exit paths
 	 * don't run into uninitialized variables. */

src/sync_p.h

@@ -61,7 +61,7 @@ typedef struct {
 	uint newuidval[2];  // UID validity obtained from driver
 	uint finduid[2];    // TUID lookup makes sense only for UIDs >= this
 	uint maxxfuid;      // highest expired UID on far side
-	uchar good_flags[2], bad_flags[2];
+	uchar good_flags[2], bad_flags[2], can_crlf[2];
 } sync_vars_t;
 
 int prepare_state( sync_vars_t *svars );