fmt.Printf: write tests for %T.

Fix a bug that caused it to ignore field widths.

R=rsc
CC=golang-dev
https://golang.org/cl/1704041

src/pkg/fmt/fmt_test.go

@@ -314,6 +314,12 @@ var fmttests = []fmtTest{
 	fmtTest{"%v", renamedComplex64(3 + 4i), "(3+4i)"},
 	fmtTest{"%v", renamedComplex128(4 - 3i), "(4-3i)"},
 
+	// %T
+	fmtTest{"%T", (4 - 3i), "complex"},
+	fmtTest{"%T", renamedComplex128(4 - 3i), "fmt_test.renamedComplex128"},
+	fmtTest{"%T", intVal, "int"},
+	fmtTest{"%6T", &intVal, "  *int"},
+
 	// erroneous things
 	fmtTest{"%d", "hello", "%d(string=hello)"},
 	fmtTest{"no args", "hello", "no args?(extra string=hello)"},

src/pkg/fmt/print.go

@@ -959,7 +959,7 @@ func (p *pp) doPrintf(format string, a []interface{}) {
 				p.buf.Write(nilAngleBytes)
 				break
 			}
-			p.buf.WriteString(reflect.Typeof(field).String())
+			p.printField(reflect.Typeof(field).String(), 's', false, false, 0)
 			continue
 		}