fmt: fix minor documentation nits

R=r, rsc
CC=golang-dev
https://golang.org/cl/4556041

src/pkg/fmt/doc.go

@@ -27,7 +27,7 @@
 		%o	base 8
 		%x	base 16, with lower-case letters for a-f
 		%X	base 16, with upper-case letters for A-F
-		%U	Unicode format: U+1234; same as "U+%0.4X"
+		%U	Unicode format: U+1234; same as "U+%04X"
 	Floating-point and complex constituents:
 		%b	decimalless scientific notation with exponent a power
 			of two, in the manner of strconv.Ftoa32, e.g. -123456p-78

src/pkg/fmt/print.go

@@ -41,7 +41,7 @@ type State interface {
 	Precision() (prec int, ok bool)
 
 	// Flag returns whether the flag c, a character, has been set.
-	Flag(int) bool
+	Flag(c int) bool
 }
 
 // Formatter is the interface implemented by values with a custom formatter.