Add some more CTL_FLAG_ABORT check points.

This should allow to abort commands doing mostly disk I/O, such as VERIFY
or WRITE SAME.  Before this change CTL_FLAG_ABORT was only checked around
data moves, which for these commands may not happen for a very long time.

MFC after:	2 weeks
Use Mt macro to properly format mailto links

Approved by:	hrs (mentor)
Execute task management request directly in ctl_queue() context.

From one side it allows to remove CTL_FLAG_TASK_PENDING flag, handling of
which significantly complicates fine-grained locking.  From the other side
it reduces task management requests latency even below then that flag could.
As downside, it denies task management code to sleep, but that is not needed
any way now.

Discussed with:	ken