The Great Rewrite (fixes #36, #61, #94, #101)

Rewrite of the file model and pulling mechanism. Needs lots of cleanup
and bugfixes, now...

cid/cid_test.go

@@ -0,0 +1,27 @@
+package cid
+
+import "testing"
+
+func TestGet(t *testing.T) {
+	m := NewMap()
+
+	if i := m.Get("foo"); i != 1 {
+		t.Errorf("Unexpected id %d != 1", i)
+	}
+	if i := m.Get("bar"); i != 2 {
+		t.Errorf("Unexpected id %d != 2", i)
+	}
+	if i := m.Get("foo"); i != 1 {
+		t.Errorf("Unexpected id %d != 1", i)
+	}
+	if i := m.Get("bar"); i != 2 {
+		t.Errorf("Unexpected id %d != 2", i)
+	}
+
+	if LocalID != 0 {
+		t.Error("LocalID should be 0")
+	}
+	if i := m.Get(LocalName); i != LocalID {
+		t.Errorf("Unexpected id %d != %c", i, LocalID)
+	}
+}