Update Buck to newest version

Now, that cross-cell support is implemented: [1] we can share rules
between projects. Cell is a container with its own buck-out directory.
The Buck design allows to replace a cell with alternative location.
This is a preparation change to support cross-cell dependencies.

The prerequisite for the hijacked cell to work properly, is that the
classpaths are always represented as absolute paths. That was not the
case in Buck implementation and thus classpath resolution across cell
boundaries was broken. This got fixed in: [2], [3].

[1] https://github.com/facebook/buck/issues/116
[2] https://github.com/facebook/buck/issues/545
[3] https://github.com/facebook/buck/pull/558

Change-Id: I3b17129c0f7ca5801f03091fff5651fb63d1482f

.buckversion

@@ -1 +1 @@
-6e4be2b06238f6dfa07cdc283255b2454d7712c6
+ca8d6cbac373a690f543c5159eec0116e76187a9

tools/eclipse/project.py

@@ -112,7 +112,8 @@ def gen_classpath():
   gwt_lib = set()
   plugins = set()
 
-  java_library = re.compile(r'[^/]+/gen/(.*)/lib__[^/]+__output/[^/]+[.]jar$')
+  # Classpath entries are absolute for cross-cell support
+  java_library = re.compile('.*/buck-out/gen/(.*)/lib__[^/]+__output/[^/]+[.]jar$')
   for p in _query_classpath(MAIN):
     if p.endswith('-src.jar'):
       # gwt_module() depends on -src.jar for Java to JavaScript compiles.