Fix PathFilterGroup not to throw StopWalkException too early

Fix PathFilterGroup not to throw StopWalkException too early

Due to the Git internal sort order a directory is sorted as if it ended
with a '/', this means that the path filter didn't set the last possible
matching entry to the correct value. In the reported issue we had the
following filters.

	org.eclipse.jgit.console
	org.eclipse.jgit

As an optimization we throw a StopWalkException when the walked tree
passes the last possible filter, which was this:
	org.eclipse.jgit.console

Due to the git sorting order, the tree was processed in this order:
	org.eclipse.jgit.console
	org.eclipse.jgit.test
	org.eclipse.jgit

At org.eclipse.jgit.test we threw the StopWalkException preventing the
walk from completing successfully.

A correct last possible match should be:
	org.eclipse.jgit/

For simplicit we define it as:
	org/eclipse/jgit/

This filter would be the maximum if we also had e.g. org and org.eclipse
in the filter, but that would require more work so we simply replace all
characters lower than '/' by a slash.

We believe the possible extra walking does not not warrant the extra
analysis.

Bug: 362430
Change-Id: I4869019ea57ca07d4dff6bfa8e81725f56596d9f