Normalize All The Path Cache Keys

Summary:
Equivalent paths do not always hash equally. When used as
hash table keys, Paths need to be normalized and either absolute or
relative to the same directory. This change normalizes the Paths used
as hash keys in the DefaultFileHashCache to ensure the cache works as
intended.

Test Plan:
0) buckd
1) buck test --all
2) add a failing assertion to a test
3) buck test --all
4) ensure that step 3 fails

src/com/facebook/buck/util/DefaultFileHashCache.java

diff --git a/src/com/facebook/buck/util/DefaultFileHashCache.java b/src/com/facebook/buck/util/DefaultFileHashCache.java
index f2d6509..7c0a98f 100644
--- a/src/com/facebook/buck/util/DefaultFileHashCache.java
+++ b/src/com/facebook/buck/util/DefaultFileHashCache.java
@@ -71,7 +71,7 @@
   public HashCode get(Path path) {
     HashCode sha1;
     try {
-      sha1 = loadingCache.get(path);
+      sha1 = loadingCache.get(path.normalize());
     } catch (ExecutionException e) {
       throw new RuntimeException(e);
     }
@@ -92,7 +92,7 @@
     if (projectFilesystem.isPathChangeEvent(event)) {
       // Path event, remove the path from the cache as it has been changed, added or deleted.
       Path path = (Path) event.context();
-      loadingCache.invalidate(path);
+      loadingCache.invalidate(path.normalize());
     } else {
       // Non-path change event, likely an overflow due to many change events: invalidate everything.
       loadingCache.invalidateAll();