Endpoints are stored according to their framework

- ImportEndpoint now contains the UID of the framework providing the end point
- ImportsRegistry now stores end points according to their framework
- ImportsRegistry now has a lost_framework(uid) method, to unregister all the
  end points from this framework at once.
  Currently, the discovery implementation (multicast) doesn't use this feature.

Also, specifications sent in packets are now formated like "python:/<spec>".
This will allow to declare a service with its Python and Java (for example) specifications:
["my.service", "java:/org.test.IMyService"] => ["python:/my.service", "java:/org.test.IMyService"]

The Java implementation of remote services will be released later, in another repository.
Decorators: Better method inheritance handling and logs

- When a callback setup find an error, the complete method description
is given (with name, source file and line) instead of just its name
- The is_from_parent method now accepts an optional value to be tested
in parameter. It ensures that the tested value comes the child class,
not from a parent one.
iPOPO: Log an error if a class is manipulated twice

When a class has two @ComponentFactory decorators, stop at the first
(lowest) one.
An error message is printed in that case.
HTTP: new servlet binding parameters

- Parameters keys are now declared in pelix.http.
- PARAM_NAME: Name of HTTP server (iPOPO instance name for the basic
implementation)
- PARAM_EXTRA: Extra properties dictionary (copy of "http.extra"
instance property for the basic implementation)
- PARAM_ADDRESS: server binding address
- PARAM_PORT: server binding port
New method accept_binding() in servlets

accept_binding(path, parameters).
Called for each new servlet registration before the path availability
check.
If it returns False, the path check is not done, avoiding to raise
unnecessary exceptions.
Else, the path is checked (possibly raising a ValueError) and, if
available, the bound_to(path, parameters) method is called.
The servlet is finally registered if bound_to does not return False.
Shell help now accepts a command name

Prints the help for the given command only
ipopo.instances and factories now print the number of computed values

Prints the number of instances (or factories) that have been found.
jPype Tutorial: Added a warning about threading
Update of the release notes for v0.5.2
Version numbers update

Ready for 0.5.2