Adds info about waiting coros.
Crash if you fail to destruct a sindex token.

This makes a very common error that I was making (failing to destruct a
sindex write token) lead to a crash rather than a deadlock. Hopefully
this will save me some pain.
Fixes a segfault and deletes a sindex_write_token.
Merge branch 'jd_coro_waiting_info' into issue_727
Thread an interruptor through.
Adds coro print script. Also adds parents to coros.
Prints the parent parameter of the coros.
Makes coros order hierarchically.
Makes coros still show index.
Makes erase range work on sindexes in a different way.
Make erase range respect the interruptor.
Fix crash when interrupting erase ranges.
adds arg checking for var arg JS API functions
Adds erase range to sindex queue.

Also adds the ability for an erase range to delay releasing the
superblock.
Removed AIOSUPPORT from the code.
Got rid of pool_io_backender_t, made io_backender_t not be a hierarchy.
Detemplatized much of linux_templated_disk_manager_t, renaming it to linux_disk_manager_t.
Made linux_file_t take a scoped_fd_t by... rvalue reference!  Egads.
Removed unused io_backend_t type.
Fixed comment to no longer reference AIO backend.