Reimplement ExportOp in a streamed fashion.

Instead of building an in-memory FeatureCollection to then be exported, use
guava's utilities to create a FeatureCollection that relies in a transforming
iterator that traverses the features in a RevTree and applied the operation
filters/transformations on the fly.
Minor fixes and changes to cli plumbing commands (blame and diff-tree)

Minor edit to documentation
added raw version to show command
Made diff-tree use plumbing DiffTree operation instead of DiffOp

Adapted functional tests for diff-tree
Fixed issues in show command
update continuous build server info in helping.rst
Merge pull request #419 from groldan/issue_85_export_oom

Reimplement ExportOp in a streamed fashion.
Avoid NPE if CTRL-D is pressed while running the console.
added logback/sl4j dependency
Use SLF4J with Logback backend as the logging framework.

The core module depends only on the slf4j API.
The cli app adds logback as a dependency specific to cli
and logs to the .geogit/log/geogit.log file.
The logback configuration file is loaded from .geogit/log/logback.xml
and a default one is created if it doesn't exist.
The location of the log file is specified in logback.xml
using the ${geogitdir} variable whose value is set to the logback
context with the result of the resolve-geogit-dir command. This way
the log file location doesn't need to be an absolute path in logback.xml
and can resolve to the correct location regardless of being at the
repository's top level directory or not.
The org.slf4j.jul-to-slf4j library is used to redirect java.util.logging
loggers (e.g. used by geotools) to logback and hence to geogit.log
Merge pull request #422 from groldan/logging_logback

Add logging to .geogit/log/geogit.log through slf4j and logback
Merge branch 'plumbing' of github.com:volaya/GeoGit into volaya-plumbing
Restore the use of checkParameter and newAnsi in Show.java
Set version to 0.6-SNAPSHOT
Add default logback.xml config file to be picked up by commands run outside a repository.
Set maven plugins version numbers.

This avoids the maven warning logs at build time complaining about
lack of version information in maven plugin declarations.
declare all depdendencies in the root pom.

All dependencies that were defined in module specific poms are now defined
in the dependencyManagement section of the root pom, and all dependency
versions are set as properties in the root pom's properties section.

This allows for an easier tracking of dependencies and versions.
Upgrade jcommander, jline, and mockito dependency numbers to their respective latests.
redirect java.util.logging loggers to slf4j even if not in a geogit directory
Make geogit-console log errors and not to fail when an exception is caught.
add missing handling of expected InvalidParameterException in geogit-console