cmd/vet: expand printf flags understood by %s and %q.

Fixes #4580.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/7002043

src/cmd/vet/print.go

@@ -208,8 +208,8 @@ var printVerbs = []printVerb{
 	{'G', numFlag},
 	{'o', sharpNumFlag},
 	{'p', "-#"},
-	{'q', "-+#."},
-	{'s', "-."},
+	{'q', " -+.0"},
+	{'s', " -+.0"},
 	{'t', "-"},
 	{'T', "-"},
 	{'U', "-#"},
@@ -282,6 +282,8 @@ func BadFunctionUsedInTests() {
 	fmt.Println("%s", "hi")            // ERROR "possible formatting directive in Println call"
 	fmt.Printf("%s", "hi", 3)          // ERROR "wrong number of args in Printf call"
 	fmt.Printf("%s%%%d", "hi", 3)      // correct
+	fmt.Printf("%08s", "woo")          // correct
+	fmt.Printf("% 8s", "woo")          // correct
 	fmt.Printf("%.*d", 3, 3)           // correct
 	fmt.Printf("%.*d", 3, 3, 3)        // ERROR "wrong number of args in Printf call"
 	fmt.Printf("%q %q", multi()...)    // ok