Linux 2.6.36 compat, use REQ_FAILFAST_MASK and remove pre-2.6.36 support

Linux 2.6.36 compat, use REQ_FAILFAST_MASK and remove pre-2.6.36 support

Commit f4af6bb783b0b7f2a6075cb1c74c225db8a157b2 which added support
for REQ_FAILFAST_MASK but the new autoconf test didn't use the same
preprocessor macro name as the code did.

The effect is that FAILFAST mode has not been enabled for ZoL in any
post-2.6.35 kernel.

Retire the HAVE_BIO_RW_FAILFAST interface used in pre-2.6.28 kernels.

Raise an error condition if the FAILFAST interface can't be detected.

Signed-off-by: Tim Chase <tim@onlight.com
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #3386