Fix file.copy recipe_module to not fail if files are already equal.

scripts/slave/recipes/chromium.expected/full_chromium_webkit_WebKit_Android__Nexus4_.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/WebKit_Android__Nexus4_",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 775 matching lines @@
       "CHROMIUM_OUTPUT_DIR": "[BUILDER_CACHE]/WebKit_Android__Nexus4_/src/out/Release",
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "PATH": "[BUILDER_CACHE]/WebKit_Android__Nexus4_/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/WebKit_Android__Nexus4_/src/build/android:%(PATH)s"
     },
     "name": "stack_tool_with_logcat_dump"
   },
   {
     "cmd": [
       "python",
       "-u",
-      "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
+      "\nimport shutil\nimport sys\n# Apparently, shutil.copy fails if files are binary-equal on *nix OSes.\n# See http://crbug.com/636168#c8.\nif hasattr(shutil, '_samefile'):\n  if shutil._samefile(sys.argv[1], sys.argv[2]):\n    sys.exit(0)\nshutil.copy(sys.argv[1], sys.argv[2])\n",
       "[BUILDER_CACHE]/WebKit_Android__Nexus4_/src/chrome/VERSION",
       "/path/to/tmp/"
     ],
     "cwd": "[BUILDER_CACHE]/WebKit_Android__Nexus4_",
     "env": {
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json",
       "PATH": "[BUILDER_CACHE]/WebKit_Android__Nexus4_/src/third_party/android_tools/sdk/platform-tools:[BUILDER_CACHE]/WebKit_Android__Nexus4_/src/build/android:%(PATH)s"
     },
     "name": "get version"
   },
@@ skipping 35 matching lines @@
       "@@@STEP_LOG_LINE@python.inline@  os.remove(report)@@@",
       "@@@STEP_LOG_END@python.inline@@@"
     ]
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]