A few classes such as Constanrs are marked with @SuppressWarnings, as are
toString() methods with many liternal, but otherwise $NLS-n$ is used for
string containing text that should not be translated. A few literals may
fall into the gray zone, but mostly I've tried to only tag the obvious
ones.

Change-Id: I22e50a77e2bf9e0b842a66bdf674e8fa1692f590

RefData now uses a sequence number as part of the field, ensuring
that updates always increase the sequence number by one whenever
a reference is modified.

Attaching a sequence number to RefData will help with storing
reference log entries during updates. As the sequence number should
be unique within the reference name space, log entries can be keyed
by the sequence number and remain unique.  Making this work over
reference delete-create cycles will require an additional RefTable
API to return the oldest sequence number previously used in the
reference log to seed the recreated reference.

Change-Id: I11cfff2a96ef962e57f29925a3eef41bdbf9f9bb
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Chris Aniszczyk <caniszczyk@gmail.com>

These types can be used by RefDatabase implementations to manage
the collection.

A RefList stores items sorted by their name, and is an immutable
type using copy-on-write semantics to perform modifications to
the collection.  Binary search is used to locate an existing item
by name, or to locate the proper insertion position if an item does
not exist.

A RefMap can merge up to 3 RefList collections at once during its
entry iteration, allowing items in the resolved or loose RefList
to override items by the same name in the packed RefList.

The RefMap's goal is O(log N) lookup time, and O(N) iteration time,
which is suitable for returning from a RefDatabase.  By relying on
the immutable RefList we might be able to make map construction
nearly constant, making Repository.getAllRefs() an inexpensive
operation if the caches are current.  Since modification is not
common, changes require up to O(N + log N) time to copy the internal
list and collapse or expand the list's array.  As most changes
are made to the loose collection and not the packed collection,
in practice most changes would require less than the full O(N)
time, due to a significantly smaller N in the loose list.

Almost complete test coverage is included in the corresponding
unit tests.  A handful of methods on RefMap are not tested in this
change, as writing the proper test depends on a future refactoring
of how the Ref class represents symbolic reference names.

Change-Id: Ic2095274000336556f719edd75a5c5dd6dd1d857
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>