DNSSEC: algorithm dependent Single-Type Signing Scheme
DNSSEC tests: algorithm dependent Single-Type Signing Scheme
fix compatibility with old compilers
review: fix comments
Merge branch 'dnssec-per-algorithm-single-type-signing' into 'master'

DNSSEC: per-algorithm Single-Type Signing

The changes enable algorithm independent Single-Type Signing Scheme support.

See merge request !315