Check type of object being written via TypedRecordOutputStream.writeObject(obj); Override Pail.toString() for nicer printing

TypedRecordOutputStream.writeObject(obj);
should check type of object being written to Pail.
Pail.toString() is also overriden to print Pail info more nicely (not just for this issue of course).

Result is following exception message:
Exception in thread "main" java.lang.IllegalArgumentException: Cannot write object SomeString of invalid type (class: java.lang.String) to pail: Pail{root='/marztest/bigdatalab/new', spec={structure=com.marcinko.bigdatalab.utils.pail.graph.DataPailStructure, args={}, format=SequenceFile}, fs=org.apache.hadoop.fs.LocalFileSystem@6fe78c96}
	at com.backtype.hadoop.pail.Pail$TypedRecordOutputStream.writeObject(Pail.java:46)