IntInSlice and StringInSlice functions

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

common/int_test.go

@@ -0,0 +1,14 @@
+package common
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIntInSlice(t *testing.T) {
+	assert.True(t, IntInSlice(1, []int{1, 2, 3}))
+	assert.False(t, IntInSlice(4, []int{1, 2, 3}))
+	assert.True(t, IntInSlice(0, []int{0}))
+	assert.False(t, IntInSlice(0, []int{}))
+}