Add cycle detection to celerity mapper

Summary: create CelerityResourceGraph, which extends AbstractDirectedGraph.
since we've done a bunch of work already to load the resource graph into memory
CelerityResourceGraph simply stores a copy and makes loadEdges work off that
stored copy.

Test Plan:
made phabricator-prefab require herald-rule-editor

~/code/phabricator> ./scripts/celerity_mapper.php webroot
Finding static resources...
Processing 154
files..........................................................................................................................................................
[2011-11-22 11:28:29] EXCEPTION: (Exception) Cycle detected in resource graph:
phabricator-prefab => herald-rule-editor => phabricator-prefab at
[/Users/btrahan/Dropbox/code/phabricator/scripts/celerity_mapper.php:173]

fixed phabricator-prefab requiring herald-rule-editor.  re-ran celerity_mapper
and no errors!

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, btrahan, epriestley

Differential Revision: 1132

src/__phutil_library_map__.php

@@ -83,6 +83,7 @@ phutil_register_library_map(array(
     'AphrontWriteGuard' => 'aphront/writeguard',
     'CelerityAPI' => 'infrastructure/celerity/api',
     'CelerityResourceController' => 'infrastructure/celerity/controller',
+    'CelerityResourceGraph' => 'infrastructure/celerity/graph',
     'CelerityResourceMap' => 'infrastructure/celerity/map',
     'CelerityStaticResourceResponse' => 'infrastructure/celerity/response',
     'ConduitAPIMethod' => 'applications/conduit/method/base',
@@ -813,6 +814,7 @@ phutil_register_library_map(array(
     'AphrontTypeaheadTemplateView' => 'AphrontView',
     'AphrontWebpageResponse' => 'AphrontResponse',
     'CelerityResourceController' => 'AphrontController',
+    'CelerityResourceGraph' => 'AbstractDirectedGraph',
     'ConduitAPI_arcanist_Method' => 'ConduitAPIMethod',
     'ConduitAPI_arcanist_projectinfo_Method' => 'ConduitAPI_arcanist_Method',
     'ConduitAPI_conduit_connect_Method' => 'ConduitAPIMethod',