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

scripts/slave/recipes/skia/swarm_test.expected/missing_SKP_VERSION_device.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[SLAVE_BUILD]/skia/tools/buildbot_spec.py",
       "/path/to/tmp/json",
       "Test-Android-GCC-Nexus7-GPU-Tegra3-Arm7-Debug"
     ],
     "cwd": "[SLAVE_BUILD]/skia",
@@ skipping 253 matching lines @@
       "PYTHONPATH": "[BUILD]/scripts",
       "SKIA_ANDROID_VERBOSE_SETUP": "1",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "push resources"
   },
   {
     "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",
       "[SLAVE_BUILD]/skia/infra/bots/assets/skp/VERSION",
       "/path/to/tmp/"
     ],
     "name": "Get downloaded SKP VERSION"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
@@ skipping 130 matching lines @@
       "GYP_DEFINES": "skia_arch_type=arm skia_warnings_as_errors=0",
       "PYTHONPATH": "[BUILD]/scripts",
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "push SKP_VERSION"
   },
   {
     "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",
       "[SLAVE_BUILD]/skia/infra/bots/assets/skimage/VERSION",
       "/path/to/tmp/"
     ],
     "name": "Get downloaded skimage VERSION"
   },
   {
     "cmd": [
       "python",
       "-u",
       "\nimport shutil\nimport sys\nshutil.copy(sys.argv[1], sys.argv[2])\n",
@@ skipping 380 matching lines @@
       "SKIA_OUT": "[SLAVE_BUILD]/out"
     },
     "name": "kill-server"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]