fixes #331

CID #1268505

Several bugs fixed:
- TCP client count can be limited by the config variable `max_tcp_clients` in `system` (so there are free descriptors for autonomous operation)
- Aggressive limits when client connects, but doesn't start sending data in time
- Throttling doesn't affect activity other then `accept()`
- Possible resource leak on `tcp_sweep`
- Bad logic (started reading from socket before checking for error activity first)
- Bad logic (could close master socket on fd exhaustion)

fixes #326 in 1.6

The limit is global, threads are allowed equal portions of the limit.

 - valgrind slowed the previous version too much

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.

Journal patches

See merge request !321

Original commits:

6319974e  Merge branch 'dnssec-per-algorithm-single-type-signing' into 'master'
13a040d8  review: fix comments
824457af  fix compatibility with old compilers
e872962e  DNSSEC tests: algorithm dependent Single-Type Signing Scheme
3c54c086  DNSSEC: algorithm dependent Single-Type Signing Scheme

7cf00157  Merge branch 'dnssec-single-type-signing' into 'master'
ae26a394  DNSSEC: single-type signing documentation
41b0aab1  tests-extra: consider single-type signing in dnskey_algorithms
17c77f4c  tests-extra: DNSSEC Single-Type Signing Schema
844b53a3  tests-extra: dnssec-verify, ignore KSK flag setting
db4d4616  DNSSEC: allow Single-Type Signing Scheme
16d2231a  DNSSEC: handle KSK and ZSK independenlty, do not sign DNSKEY with ZSK

Correct detection of journal end position.

4a21001f  Merge branch 'journal_file_end_check' into 'master'
1b07a798  journal: correct file end position detection
fbc46902  tests: journal, added 10x rollover, random item size

refs #309

Original commits:

079427a5  journal: fix possible journal size retrieval race
c329558a  Merge branch 'journal_fsize' into 'master'
4f7b8404  journal: prevent unlimited growth on shrinking/overfill

Reported-by: Philip Paeps

Included changes:

- log warnings properly
- issue warning when FQDN retrieval fails for system.identity and system.nsid
- cache hostname lookup

refs #306

Original commits:

9de0e69e  Merge branch 'conf-hostname-error' into 'master'
7bcf3ff3  log: cache hostname lookup for nsid and identity
9ab4ea4f  log: warn on error retrieving auto value for NSID and identity
3ad605d6  log: update warnings to use cf_warning
87b7676c  conf: added cf_warning API

expire zone when XFR is failing

fixes #304

See merge request !297

Forced refresh fix

Fixes #303

See merge request !298