Added remote service endpoint name reuse

- When a service is unregistered, or updates its endpoint name, its
  previous name can now be reused immediatly by another service.
- fixes #17
Corrected format strings arguments
Added a CountdownEvent class to pelix.utilities

An Event which is set once its internal counter reaches 0.
Enhanced thread pool's FutureResult to support a callback method

Instead of "actively" waiting for the result to come, a method can be
set via FutureResult.set_callback(). This method will be called once the
execution is done or in case of error.
An extra parameter can be given to the called back method.
Tests and corrections for EventData and CountdownEvent
Added tests for the new features of FutureResult
Added pylint comments to remove false-positives

- Python 2-3 modules import errors/failures are now quiet
- PyLint seems to have problem checking "raise ex" instructions
- Removed the "duplicate code" warning
Corrected IPv6 double stack activation calls

The utility method set_double_stack() was given the socket module,
instead of self.socket... :/
Ignore PyCharm project folder
EventData: Clear the exception field when calling set()
Code review according to PyCharm

- Corrected risks of unbound variables
Forget previous global members in Bundle.update()

- Python's reload() or imp.reload() keeps old/non-overridden global variables in the module dictionary
  => if a class or method is renamed, its old version was still available with its old name
- This commit ensures that only special members ("__some_name__") are kept while using Bundle.update()
- This fixes #24
Removed the ununsed "stop" parameter of stop()
Bundle.update(): reset module dict members on error

If the call to reload() fails (syntax error, file missing, ...), the previous content of the module must be restored
Added support for synonyms (remote services)

fixes #19
Added client-side tests for Remote Services

- Testing client-side of XML/JSON/JABSORB-RPC transport
  (server-side tested de facto)
- Using multicast for discovery
Added jsonrpclib-pelix installation for Travis
Delete local framework in case of start error
jsonrpclib-pelix must be installed in tox environment, not in Travis
Forgot jsonrpclib-pelix in Tox for Python 2.6