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/testdata/foobar/foo.go

@@ -0,0 +1,7 @@
+package foobar
+
+// OtherBool ...
+func OtherBool() bool {
+	ok := getBool()
+	return ok
+}