After creating a Transport instance callers should always call
its close() method. Use AutoCloseable to document this idiom
and allow use of try-with-resources.

Change-Id: I0c6ff3e39ebecdd7a028dbcae1856a818937b186

Since git-core ff5effd (v1.7.12.1) the native wire protocol transmits
the server and client implementation and version strings using
capability "agent=git/1.7.12.1" or similar.

Support this in JGit and hang the implementation data off UploadPack
and ReceivePack.  On HTTP transports default to the User-Agent HTTP
header until the client overrides this with the optional capability
string in the first line.

Extract the user agent string into a UserAgent class under transport
where it can be specified to a different value if the application's
build process has broken the Implementation-Version header in the
JGit package.

Change-Id: Icfc6524d84a787386d1786310b421b2f92ae9e65

Any messages received on side band #2 that aren't scraped as a
progress message into our ProgressMonitor are now forwarded to a
buffer which is later included into the OperationResult object.
Application callers can use this buffer to present the additional
messages from the remote peer after the push or fetch operation
has concluded.

The smart push connections using the native send-pack/receive-pack
protocol now request side-band-64k capability if it is available
and forward any messages received through that channel onto this
message buffer.  This makes hook messages available over smart HTTP,
or even over SSH.

The SSH transport was modified to redirect the remote command's
stderr stream into the message buffer, interleaved with any data
received over side band #2.  Due to buffering between these two
different channels in the SSH channel mux itself the order of any
writes between the two cannot be ensured, but it tries to stay close.

The local fork transport was also modified to redirect the local
receive-pack's stderr into the message buffer, rather than going to
the invoking JVM's System.err.  This gives applications a chance
to log the local error messages, rather than needing to redirect
their JVM's stderr before startup.

To keep things simple, the application has to wait for the entire
operation to complete before it can see the messages.  This may
be a downside if the user is trying to debug a remote hook that is
blocking indefinitely, the user would need to abort the connection
before they can inspect the message buffer in any sort of UI built
on top of JGit.

Change-Id: Ibc215f4569e63071da5b7e5c6674ce924ae39e11
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

As discussed on the egit-dev mailing list, we prefer not to have
trailing whitespace in our source code.  Correct all currently
offending lines by trimming them.

Change-Id: I002b1d1980071084c0bc53242c8f5900970e6845
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>