testing: fix error message on invalid regexp

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/3831041

src/pkg/testing/benchmark.go

@@ -175,7 +175,7 @@ func RunBenchmarks(matchString func(pat, str string) (bool, os.Error), benchmark
 	for _, Benchmark := range benchmarks {
 		matched, err := matchString(*matchBenchmarks, Benchmark.Name)
 		if err != nil {
-			println("invalid regexp for -benchmarks:", err)
+			println("invalid regexp for -benchmarks:", err.String())
 			os.Exit(1)
 		}
 		if !matched {

src/pkg/testing/testing.go

@@ -144,7 +144,7 @@ func Main(matchString func(pat, str string) (bool, os.Error), tests []InternalTe
 	for i := 0; i < len(tests); i++ {
 		matched, err := matchString(*match, tests[i].Name)
 		if err != nil {
-			println("invalid regexp for -match:", err)
+			println("invalid regexp for -match:", err.String())
 			os.Exit(1)
 		}
 		if !matched {