crypto: comment change on disabling compression

This is a comment change, where it originally says disabling TLS
Compression protects against BEAST attack. But in fact, it is the
CRIME attack(Compression Ratio Info-leak Made Easy) that makes use
of TLS Compression and not BEAST.

BEAST(Browser Exploit Against SSL/TLS) is an entirely another variant
making use of the chosen boundary attack against CBC mode in
encryption.

Just making sure, that the exact reason for disabling TLS compression
must be made clear and not be misleading with some other attack.
fs: move makeCallback and maybeCallback to util

`makeCallback()`, `maybeCallback()`, and `rethrow()` declared in fs
can also be used in other places.