Add more opcodes so we can read Graphite's Carbon stream

This adds support for enough opcodes to unpickle a graphite rendering
message, described at
http://graphite.readthedocs.org/en/0.9.10/render_api.html#pickle.

I also made some internal changes to consistently report errors to the
main decoding loop and renamed 'append' to 'push' so as not to conflict
with Go's builtin append keyword.  The unit tests still pass, and there
are now two tests for sample graphite pickles too.

ogórek_test.go

@@ -2,6 +2,7 @@ package ogórek
 
 import (
 	"bytes"
+	"encoding/hex"
 	"math/big"
 	"reflect"
 	"testing"
@@ -59,6 +60,9 @@ func TestMarker(t *testing.T) {
 	}
 }
 
+var graphitePickle1, _ = hex.DecodeString("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")
+var graphitePickle2, _ = hex.DecodeString("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")
+
 func TestDecode(t *testing.T) {
 	tests := []struct {
 		name     string
@@ -79,6 +83,8 @@ func TestDecode(t *testing.T) {
 		{"unicode", "V\\u65e5\\u672c\\u8a9e\np0\n.", string("日本語")},
 		{"empty dict", "(dp0\n.", make(map[interface{}]interface{})},
 		{"dict with strings", "(dp0\nS'a'\np1\nS'1'\np2\nsS'b'\np3\nS'2'\np4\ns.", map[interface{}]interface{}{"a": "1", "b": "2"}},
+		{"graphite message1", string(graphitePickle1), []interface{}{map[interface{}]interface{}{"values": []interface{}{float64(473), float64(497), float64(540), float64(1497), float64(1808), float64(1890), float64(2013), float64(1821), float64(1847), float64(2176), float64(2156), float64(1250), float64(2055), float64(1570), None{}, None{}}, "start": int64(1383782400), "step": int64(86400), "end": int64(1385164800), "name": "ZZZZ.UUUUUUUU.CCCCCCCC.MMMMMMMM.XXXXXXXXX.TTT"}}},
+		{"graphite message2", string(graphitePickle2), []interface{}{map[interface{}]interface{}{"values": []interface{}{float64(473), float64(497), float64(540), float64(1497), float64(1808), float64(1890), float64(2013), float64(1821), float64(1847), float64(2176), float64(2156), float64(1250), float64(2055), float64(1570), None{}, None{}}, "start": int64(1383782400), "step": int64(86400), "end": int64(1385164800), "name": "user.login.area.machine.metric.minute"}}},
 	}
 	for _, test := range tests {
 		buf := bytes.NewBufferString(test.input)
@@ -88,7 +94,7 @@ func TestDecode(t *testing.T) {
 			t.Error(err)
 		}
 		if !equal(v, test.expected) {
-			t.Errorf("%s: got %q expected %q", test.name, v, test.expected)
+			t.Errorf("%s: got\n%q\n expected\n%q", test.name, v, test.expected)
 		}
 	}
 }