compiler: move tests from vm/tests

These don't belong to VM as they compile some Go code and run it in a VM. One
may call them integration tests, but I prefer to attribute them to
compiler. Moving these tests into pkg/compiler also allows to properly count
the compiler coverage they add:

-ok     github.com/CityOfZion/neo-go/pkg/compiler       (cached)        coverage: 69.7% of statements
+ok     github.com/CityOfZion/neo-go/pkg/compiler       (cached)        coverage: 84.2% of statements

This change also fixes `contant` typo and removes fake packages exposed to the
public by moving foo/bar/foobar into the testdata directory.

pkg/compiler/if_test.go

@@ -0,0 +1,93 @@
+package compiler_test
+
+import (
+	"math/big"
+	"testing"
+)
+
+func TestLT(t *testing.T) {
+	src := `
+		package foo
+		func Main() int {
+			x := 10
+			if x < 100 {
+				return 1
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestGT(t *testing.T) {
+	src := `
+		package testcase
+		func Main() int {
+			x := 10
+			if x > 100 {
+				return 1
+			}
+			return 0
+		}
+	`
+	eval(t, src, []byte{})
+}
+
+func TestGTE(t *testing.T) {
+	src := `
+		package testcase
+		func Main() int {
+			x := 10
+			if x >= 100 {
+				return 1
+			}
+			return 0
+		}
+	`
+	eval(t, src, []byte{})
+}
+
+func TestLAND(t *testing.T) {
+	src := `
+		package testcase
+		func Main() int {
+			x := 10
+			if x >= 10 && x <= 20 {
+				return 1
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestLOR(t *testing.T) {
+	src := `
+		package testcase
+		func Main() int {
+			x := 10
+			if x >= 10 || x <= 20 {
+				return 1
+			}
+			return 0
+		}
+	`
+	eval(t, src, big.NewInt(1))
+}
+
+func TestNestedIF(t *testing.T) {
+	src := `
+		package testcase
+		func Main() int {
+			x := 10
+			if x > 10 {
+				if x < 20 {
+					return 1
+				}
+				return 2
+			}
+			return 0
+		}
+	`
+	eval(t, src, []byte{})
+}