These methods allow to find all configuration entry names for a given
section or section/subsection searching recursively through all base
configurations of the given configuration.

These methods are needed to calculate the names for the effective
configuration of a git repository which combines the configuration entry
names found in the repository, global and system configuration files

Bug: 396659
Change-Id: Ie3731b5e877f8686aadad3f1a46b2e583ad3b7c6
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

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

Instead of indexing the subsection names on each request for a given
section name, index both the section and subsection names in a single
scan through the entry list. This should improve lookup time for
reading the section names out of the configuration, especially for the
url.*.insteadof type of processing performed in RemoteConfig.

Change-Id: I7b3269565b1308f69d20dc3f3fe917aea00f8a73

Decrease running time for getStringList (and all other get methods) by
looking for configuration entries using binary search rather than
linear search through the configuration file.

Configuration lines are sorted by section, subsection, name in a
sorted list whenever the snapshot is rebuilt. Binary search is used to
locate an index in the middle of the values, then walk backwards to
find the first value in the range.

Given a configuration of file of 5000 distinct section/subsection/name
triplets (e.g. a Gerrit Code Review project.config configuration file
with 5000 unique access control rules), this new code is faster to
lookup each rule individually using getStringList():

  old setStringList() 194 usec avg
      getStringList() 196 usec avg

  new setStringList() 188 usec avg
      getStringList()  24 usec avg

Change-Id: Ic8907231868c18eb946b72f341a6b58666b70324

The Config class is getting very large. Extract two of its inner
classes into new top level types to reduce the size of Config.
Rename them slightly in the process.

Change-Id: I693148a5ae2977378789bf455c880a6fd856c0f0

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>