GM self-tests: add testing for non --hierarchy case

gm/tests/outputs/no-hierarchy/output-expected/json-summary.txt

Index: gm/tests/outputs/no-hierarchy/output-expected/json-summary.txt
===================================================================
--- gm/tests/outputs/no-hierarchy/output-expected/json-summary.txt	(revision 0)
+++ gm/tests/outputs/no-hierarchy/output-expected/json-summary.txt	(revision 0)
@@ -0,0 +1,25 @@
+{

[epoger, 2013/05/19 08:06:20]

confirmation that this is correct:

$ diff
gm/tests/outputs/compared-against-different-pixels-json/output-expected/json-summary.txt
gm/tests/outputs/no-hierarchy/output-expected/json-summary.txt 
4c4
<          "565/selftest1.png" : {
---
7c7
<          "8888/selftest1.png" : {
---
16c16
<       "565/selftest1.png" : {
---
20c20
<       "8888/selftest1.png" : {
---

+   "actual-results" : {
+      "failed" : {
+         "selftest1_565.png" : {
+            "bitmap-64bitMD5" : 12927999507540085554
+         },
+         "selftest1_8888.png" : {
+            "bitmap-64bitMD5" : 1209453360120438698
+         }
+      },
+      "failure-ignored" : null,
+      "no-comparison" : null,
+      "succeeded" : null
+   },
+   "expected-results" : {
+      "selftest1_565.png" : {
+         "allowed-bitmap-64bitMD5s" : [ 8863920166200910451 ],
+         "ignore-failure" : false
+      },
+      "selftest1_8888.png" : {
+         "allowed-bitmap-64bitMD5s" : [ 13451349865803053525 ],
+         "ignore-failure" : false
+      }
+   }
+}