Applies some special transformation or filtering to the original Entry.
original - The original Entry that was read and parsed from
the input file.
firstLineNumber - The first line number of the LDIF record
corresponding to the read Entry. This is most
useful when throwing an LDIFException.
The Entry that should be returned in the call to
LDIFReader.readEntry(). This can be the original parameter
Entry, a newly constructed Entry, or null to signal that
the provided Entry should be skipped.
LDIFException - If there is an exception during processing. This
exception will be re-thrown to the caller of