move libversions check out of precommit to another target? [LUCENE-6018]

The libversions check can be especially heavy (taking minutes and downloading a lot?). Lately, i cannot get it to finish. To run precommit checks i have to hack build.xml and then revert it.

Can we move this from precommit to another target? A few things:
1. i dont think most commits contain changes to third party dependencies, so it discourages precommit, which is already hard to get people to run.
2. most commits that DO contain changes to third party dependencies, the people committing them don't run precommit before doing so. We know this from the jenkins fails that happen.
3. really, for a "packaging" change like dependencies nightly-smoke is the one to run to get best verification.

We should do the same for other problematic targets, I know i opened an issue for the jtidy one... that is still unresolved.

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Migrated from [LUCENE-6018](https://issues.apache.org/jira/browse/LUCENE-6018) by Robert Muir (@rmuir)

Start in build.xml by locating the precommit target and its libversions check, then inspect the nightly-smoke target and the Jenkins failures described in the issue. Determine where the check should run instead; done means ordinary precommit no longer performs the heavy check while dependency changes still receive the intended verification.

Written by the indexing model from the issue text.