Reintroduce protected method which removal broke EMF Compare

Reintroduce protected method which removal broke EMF Compare

So far we follow OSGi semantic versioning [1] which says the following:

"A change in the second (minor) part of the version signals that the
change is backward compatible with consumers of the API package but not
with the providers of that API. That is, when the API package goes from
version 1.5 to 1.6 it is no longer compatible with a provider of that
API but consumers of that API are backward compatible with that API
package."

The change Ib5fbf17bdaf727bc5d0e106ce88f2620d9f87a6f broke EMF Compare
which subclasses ResolveMerger since we added a new parameter to the
protected ResolveMerger.processEntry() method. According to the above
cited OSGi semantic versioning this is ok, implementers should expect
that they break on minor version changes of the API they implement.

This change reintroduces the old processEntry() method in order to help
avoid breakage for existing EMF Compare versions which expect breakage
also for the implementer case only for major version change (in this
case from JGit 4.x to 5.x).

[1] http://www.osgi.org/wp-content/uploads/SemanticVersioning1.pdf

See: https://dev.eclipse.org/mhonarc/lists/jgit-dev/msg03431.html
Change-Id: I48ba4308dee73925fa32d6c2fd6b5fd89632c571
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>