this is to guarantee that there is at least one vacant entry between the
qtail and the qhead

this fixes an issue when the end-of-file was encountered not before, but
during node eviction

this reuses maximum amount of space after flush

the free space is at the end of file if:
- the file is empty OR
  - qhead.pos <= qtail.pos
  - free.pos > qtail.pos

tests: added randomized values per each read/write

Resolve valgrind slowdown by waiting for all expectedly valid zones.

We should rather wait till the server initialization is done, but this
is not possible at the moment.

namedb:
- API change, ported timers and test
namedb_lmdb:
- support for variable map_size, env/db flags
- multiple dbs, shared environment support
namedb_trie:
- configurable bucket size

DNSSEC: per-algorithm Single-Type Signing

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

See merge request !315

Correct detection of journal end position.

MR !316

This fixes an issue where the journal file could grow over the set
limit if:
1. Last entry on previous rollover did not fill the file fully
2. The information about the difference between the last entry and the
file size is lost

In such case, the end of file is detected later, leading to
increase of the file size by the size of the first evicted entries.

lookup table: checking parameters
serial compare: legal corner cases proper testing
                (Maybe they should be ommited, because it would
                also be legal if the comparisons had opposite
                results. But at least we will know if we change
                something.)

TODO: Handle the undefined corner cases of serial difference.
TODO: NULL arguments to lookup table?

refs #309

See merge request !313

DNSSEC: Single-Type Signing

See merge request !312

refs #309