fix some typos
pack pointers by casting them to size_t
reorganize file tests and run them in both sync and async mode
some handy cmp extensions
increase delay scale because the test became fragile (it was too low)
async versions of stat, lstat, lseek, read, close

the file routines detect if they are running in a coroutine (in other words,
under the scheduler) and use non-blocking, async variants in that case