Added cache-resyncing to ProcPool. This makes sure to update all affected object caches

whenever the subprocess returns (this is potentially not good enough for long-running scripts,
will have to ponder that one). Made ProcPool work with MySQL (where it works much better). Tested and fixed many
small bugs.

src/__init__.py

@@ -0,0 +1,2 @@
+# experimental central dictionary for models in subprocesses to report they have been changed.
+PROC_MODIFIED_OBJS = []