CRUNCH-291 Add toString method on CrunchInputSplit
CRUNCH-289 Allow materializing Avro SpecificRecords

Due to issues outlined in AVRO-1240, the correct classloader must
be supplied to the SpecificData class to allow reading
SpecificRecords. This patch passes a custom classloader to the
SpecificData constructor to allow locally materializing
SpecificRecords when running with "hadoop jar".