Mark morphology test as expected-to-fail for poppler.

expectations/gm/Test-Ubuntu12-ShuttleA-ATI5770-x86_64-Debug/expected-results.json

 {
   "actual-results": {
     "failed": null, 
     "failure-ignored": null, 
     "no-comparison": null, 
     "succeeded": null
   }, 
   "expected-results": {
     "3x3bitmaprect_565.png": {
       "allowed-digests": [
@@ skipping 7771 matching lines @@
       "ignore-failure": false
     }, 
     "morphology_pdf-poppler.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           15089079208206756723
         ]
       ], 
       "bugs": [
-        1578
+        1657
       ], 
+      "ignore-failure": true, 
       "reviewed-by-human": false
     }, 
     "nested_aa_565.png": {
       "allowed-digests": [
         [
           "bitmap-64bitMD5", 
           14872504505116457825
         ]
       ], 
       "bugs": [
@@ skipping 3123 matching lines @@
           "bitmap-64bitMD5", 
           4745935902621983993
         ]
       ], 
       "bugs": [
         1578
       ], 
       "reviewed-by-human": false
     }
   }
-}
+}