Intermittent exc in TestIndexWriter.testAddDocumentOnDiskFull [LUCENE-2698]

3.x build just hit this:
```
Stacktrace

junit.framework.AssertionFailedError
at org.apache.lucene.util.LuceneTestCase$LuceneTestCaseRunner.runChild(LuceneTestCase.java:693)
at org.apache.lucene.util.LuceneTestCase$LuceneTestCaseRunner.runChild(LuceneTestCase.java:666)
at org.apache.lucene.index.TermVectorsReader.(TermVectorsReader.java:91)
at org.apache.lucene.index.SegmentReader$CoreReaders.openDocStores(SegmentReader.java:304)
at org.apache.lucene.index.SegmentReader.get(SegmentReader.java:585)
at org.apache.lucene.index.SegmentReader.get(SegmentReader.java:561)
at org.apache.lucene.index.DirectoryReader.(DirectoryReader.java:102)
at org.apache.lucene.index.ReadOnlyDirectoryReader.(ReadOnlyDirectoryReader.java:27)
at org.apache.lucene.index.DirectoryReader$1.doBody(DirectoryReader.java:78)
at org.apache.lucene.index.SegmentInfos$FindSegmentsFile.run(SegmentInfos.java:692)
at org.apache.lucene.index.DirectoryReader.open(DirectoryReader.java:72)
at org.apache.lucene.index.IndexReader.open(IndexReader.java:344)
at org.apache.lucene.index.IndexReader.open(IndexReader.java:230)
at org.apache.lucene.index.TestIndexWriter.testAddDocumentOnDiskFull(TestIndexWriter.java:515)
Standard Output

NOTE: reproduce with: ant test -Dtestcase=TestIndexWriter -Dtestmethod=testAddDocumentOnDiskFull -Dtests.seed=3136129128141482592:-2364438756268371069
NOTE: test params are: locale=nl_BE, timezone=Asia/Tel_Aviv
```

---
Migrated from [LUCENE-2698](https://issues.apache.org/jira/browse/LUCENE-2698) by Michael McCandless (@mikemccand)

Start with TestIndexWriter.testAddDocumentOnDiskFull and reproduce it using the reported ant command and seed. Trace the failure through TermVectorsReader, SegmentReader, DirectoryReader, and IndexReader using the provided stack trace. Done means the intermittent exception is understood and the disk-full test completes reliably.

Written by the indexing model from the issue text.