Lucene puts output of svnversion into a property even if svnversion failed [LUCENE-4073]

We had a build issue today where Lucene was running svnversion which was failing (the reason for the failure itself is not particularly important.)

As a result, the error text output of running the command ended up in the svnversion property. The build later attempted to insert this into MANIFEST.MF which resulted in an invalid manifest file, causing the build to fail.

A related observation is that even if it works, the svnversion would be the version of our own repository, so the usefulness of it in the context of Lucene's version number is questionable anyway. It would be nice if the build could get the svn version number only if it was checked out from Lucene trunk.

---
Migrated from [LUCENE-4073](https://issues.apache.org/jira/browse/LUCENE-4073) by Trejkaz, updated Sep 08 2014
Environment:
```
Windows 7 x64, Cygwin for tools like svn
```

Linked issues:
- #6656