Version mutations aren't cleared out by delete records where

[alecgrieser]

Versionstamp-related mutations are currently stored in a buffer in the JVM and flushed during commit. This is to support multiple updates to the same record happening during a single transaction. Right before commit, this data is flushed to disk.

However, this data structure is not cleared out when there is a deleteRecordsWhere operation. This means that if one:

1. Inserts a record with a versionstamp then
2. Issues a deleteRecordsWhere operation for that record, the result is
3. The versionstamp (and versionstamp indexes) get inserted into the database, but the record itself does not

This leads to a missing split point exception when the record is read. As a fix, the versionstamp keys should be cleared out during deleteRecordsWhere as well. Alternatively, we could ban deleteRecordsWhere if there are outstanding versionstamp operations.