BUG #12826: Streaming replication - should master/slave file system be identical?

The following bug has been logged on the website:

Bug reference:      12826
Logged by:          Jamie Koceniak
Email address:      jkoceniak@mediamath.com
PostgreSQL version: 9.1.14
Operating system:   Linux
Description:        

Should the file system between a PG master and slave be identical?
When I do an audit of the PG file system (i.e.
postgresql/9.1/main/base/31858), I see _fsm files that exist on the slave
but don’t exist on the master. I also see _fsm & _vm files on the master
that are not on the slave.

Besides doing basic table row counts between a master and slave, how do you
verify that the master and slave are in synch when using streaming
replication?