sshd does support gssapi-with-mic on the server side, but has no
built-in client-side support for this authentication mechanism.

Add our own implementation for it, following RFC 4462.[1] To avoid
needlessly re-trying mechanisms that aren't even configured on the
client, we disable mechanisms that fail on the very first attempt
to use them.

Since we have no real Kerberos5 test setup, this cannot be fully
tested in CI. The disabling of the authentication mechanism and
that it is skipped when not successful _is_ tested.

[1] https://www.ietf.org/rfc/rfc4462.txt

Bug: 520927
Change-Id: I5d0cdb14103588a57c52f927df541b589ab88d88
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Add a new ssh client implementation based on Apach MINA sshd 2.0.0.

This implementation uses JGit's own config file parser and host entry
resolver. Code inspection of the Apache MINA implementation revealed
a few bugs or idiosyncrasies that immediately would re-introduce bugs
already fixed in the past in JGit.

Apache MINA sshd is not without quirks either, and I had to configure
and override more than I had expected. But at least it was all doable
in clean ways.

Apache MINA boasts support for Bouncy Castle, so in theory this should
open the way to using more ssh key algorithms, such as ed25519.

The implementation is in a separate bundle and is still not used in
the core org.eclipse.jgit bundle. The tests re-use the ssh tests from
the core test bundle.

Bug: 520927
Change-Id: Ib35e73c35799140fe050d1ff4fb18d0d3596580e
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>

Change-Id: Ifcb9c67daeb9da84a1461a4f731523ac5df3a223
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

Replace the old crude event listener system with a much more generic
implementation, patterned after the event dispatch techniques used
in Google Web Toolkit 1.5 and later.

Each event delivers to an interface that defines a single method,
and the event itself is what performs the delivery in a type-safe
way through its own dispatch method.

Listeners are registered in a generic listener list, indexed by
the interface they implement and wish to receive an event for.
Delivery of events is performed by looping through all listeners
implementing the event's corresponding listener interface, and using
the event's own dispatch method to deliver the event.  This is the
classical "double dispatch" pattern for event delivery.

Listeners can be unregistered by invoking remove() on their
registration handle.  This change therefore requires application
code to track the handle if it wishes to remove the listener at a
later point in time.

Event delivery is now exposed as a generic public method on the
Repository class, making it easier for any type of message to
be sent out to any type of listener that has registered, without
needing to pre-arrange for type-safe fireFoo() methods.

New event types can be added in the future simply by defining a
new RepositoryEvent subclass and a corresponding RepositoryListener
interface that it dispatches to.  By always adding new events through
a new interface, we never need to worry about defining an Adapter
to provide default no-op implementations of new event methods.

Change-Id: I651417b3098b9afc93d91085e9f0b2265df8fc81
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

Per CQ 3448 this is the initial contribution of the JGit project
to eclipse.org.  It is derived from the historical JGit repository
at commit 3a2dd9921c.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>