SWMR issues and atomic failures

Answering my own question, to test atomic operations, follow the documentation test/AtomicWriterReader.txt. Would be nice if the automated "make check" performed this test and came back with a FAILED message, but that's OK for now.

Results on Fedora 22 x86_64:

Ext3/4 failed as expected.
JFS: failed
BTRFS: failed
VFAT: failed