SQUASH/job_wait: clarify return value
job: increase JOB_BUFFER_SIZE to 0xFFFF

It used to be 1024 bytes, which is very tiny and slows down some operations
(imaging `cat`-ing a large file). Benchmarks show a large speedup for such
cases. ref #978.

For modern systems 0xFFFF bytes (65535 B = 64 KB = 0.0625 MB) per job
shouldn't be a big problem.
rstream: remove 'reading' struct member

Not necessary, as discussed in #980.

Closes #980.