compiler: use fully-qualified names for tracking functions

Function name now consists of 3 parts:
1) full package path
2) method receiver type (if any)
3) function name itself .

Fix #1150.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

pkg/compiler/testdata/foo/foo.go

@@ -4,3 +4,16 @@ package foo
 func NewBar() int {
 	return 10
 }
+
+// Foo is a type.
+type Foo struct{}
+
+// Bar is a function.
+func Bar() int {
+	return 1
+}
+
+// Bar is a method.
+func (f Foo) Bar() int {
+	return 8
+}