New annotation class: file-parallel and read-only

[angelhof]

Based on the discussions of the Annotations working group, we believe we will need a couple of new classes annotations for non-parallelizable pure and side-effectful commands. The first additional annotation would describe a subclass of non-parallelizable pure and side-effectful commands that are safe to parallelize across file boundaries (allowing parallelization of for, xargs, and other similar constructs). The second class would be side-effectful commands that only read environment variables—including hardware properties, /proc filesystem etc.

[angelhof]

Ported from: binpash/pash#281