IntInSlice and StringInSlice functions

Refs https://github.com/tendermint/tendermint/pull/835

common/string.go

@@ -43,3 +43,13 @@ func StripHex(s string) string {
 	}
 	return s
 }
+
+// StringInSlice returns true if a is found the list.
+func StringInSlice(a string, list []string) bool {
+	for _, b := range list {
+		if b == a {
+			return true
+		}
+	}
+	return false
+}