* async generators: much better stack traces
* dav: use global identity system rather than login/logout to manage
usernames and passwords.
* dav: there is a checkLogin() instead of login() which can be used to
verify auth at any time.
* dav: make it so that we can (only internally atm) hold multiple
locks for different URLs.
* identity: add an identity manager singleton service to keep
identities globally, referenced by a name, with aliasing support (so
e.g., dav can ask for the 'dav' identity, while something else can
alias 'dav' to another identity).
* service: keep track of logged in status here, rather than in the dav
service. Use the global id manager.
* Logging improvements / default log levels tweaked. Less chatty now.
Ability to tweak log levels of individual loggers via prefs.
* Various crypto module fixes, specially for RSA.
* 'service' lock removed, reuses server lock now. dav module supports
temporarily blocking locks to simulate the 'service' lock (login()
needs this, since dav is not configured at that time).
* PKI support: data encryption uses randomly-generated symmetric keys,
which are then encrypted with RSA public keys and stored on the
server.
* Async helpers are in a module of their own now
* Async routines have simpler semantics now. onComplete handlers are taken care of by the helpers. Exceptions are bubbled up across nested asynchronous generators
* Stack traces are automatically logged for unhandled exceptions
* Async generators are now allowed to 'bottom out' (StopIteration is ignored) - this is configurable.
* RSA key generation fixes
* On login we now create an RSA keypair, encrypt the private one with PBE, and upload them to the server
* Log files are now limited to 2MB (down from 5)
