Don't use # in cache keys; http throws away the suffix

Testing Done:
CI passes.

Bugs closed: pantsbuild#184

Reviewed at https://rbcommons.com/s/twitter/r/453/

pants.ini

@@ -28,7 +28,7 @@ write_artifact_caches: []
 # Mixed into all cache keys. Bump this to invalidate all existing artifacts.
 # Note: If you want to experiment with this locally without affecting artifacts
 # read by all, change it to some other string, e.g., <number>-<your username>.
-cache_key_gen_version: '100'
+cache_key_gen_version: '200'
 
 jvm_args: ['-Xmx1g', '-XX:MaxPermSize=256m']
 

src/python/pants/base/build_invalidator.py

@@ -87,7 +87,7 @@ def key_for_target(self, target, transitive=False, fingerprint_strategy=None):
       target_key = target.transitive_invalidation_hash(fingerprint_strategy)
     else:
       target_key = target.invalidation_hash(fingerprint_strategy)
-    full_key = '{target_key}#{key_suffix}'.format(target_key=target_key, key_suffix=key_suffix)
+    full_key = '{target_key}_{key_suffix}'.format(target_key=target_key, key_suffix=key_suffix)
     return CacheKey(target.id, full_key, target.payload.num_chunking_units, (target.payload,))