treat tab just like space in dc input rather than printing
	11 is unimplemented

Reference: /n/sources/patch/applied/dctab
Date: Sat Dec 11 19:16:12 CET 2010
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/dc.c	Sat Dec 11 19:15:39 2010
+++ /sys/src/cmd/dc.c	Sat Dec 11 19:15:36 2010
@@ -213,6 +213,7 @@
 		}
 		switch(c) {
 		case ' ':
+		case '\t':
 		case '\n':
 		case -1:
 			continue;