void return types 'return no value'. This is obvious and therefore
unneccessary to mention.
We spare rewind(3)'s sentence because espie@ pointed out that it's a
warning - the function masks a potential error.
This commit also adds a sentence to X509_free clarifying that it's
NULL-safe. This bit was discussed with doug@.
ok martijn@, sentiment supported by schwarze@

OK jmc

Not sure what's more surprising: how long it took for NetBSD to
catch up to the rest of the BSDs (including UCB), or the amount of
code that NetBSD has claimed for itself without attributing to the
actual authors.
OK deraadt@

fixes pr #4996, from joachim schipper;

- break long lines
ok jmc

Now passes the regress tests.