Updating JaCoCo in commit 23072ffb broke the build of the
HTML documentation. As found out by @chirontt, adding parboiled
as a build dependency fixes it.

Fixes #1220 and closes #1313

This reverts commit 662fb9012f.

To be able to read and migrate Lucene indices from old (4.x)
formats to new (5.x) ones, add the `lucene-backward-codecs`
library to the project.
It is added to the `ext` directory and therefore to the classpath.
According to the Lucene documentation, having it in the classpath
can affect performance. But right now the `ext` directory is the
only one available and even for a separate tool for offline
migration the library would be needed.

Exclude Lucene dependencies `lucene-spatial` and `lucene-join`.
They were added during the update but are not needed. This patch
excludes them explicitly so that they do not show up in the
generated IDE files and `ext` directory.

Bump version to 1.9.0-SNAPSHOT, increasing the minor as the next
release includes interface changes.

Use explicit coordinates, and therefor version numbers fro JUnit
in the build.moxie file. It should not be some version that just
happens to be used.

Update JUnit to latest 4.12.
Update JaCoCo to lates 0.7.8, which makes it work under Java 8.
The last used version would fail when tests are run under Java 8.

This reverts commit 55c385e96e6594ec1ac3b5cd41ccd2df6048b696, reversing
changes made to 61bb29d492.

JGit 4.0.0 fixes a memory leak but introduces a non-compatible change
for closing the RevWalk: before it was release() but now is close()