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()

Also switch back to Maven Central repository.