dnsdist: Don't cache ServFail / Refused if the TTL is set to 0

Merge pull request #4985 from rgacogne/write-single-syscall

Add `sendSizeAndMsgWithTimeout` to send size and data in a single call

Merge pull request #4986 from rgacogne/travis-build-dir

Use `${TRAVIS_BUILD_DIR}` instead of assuming the repo is in `pdns`

Merge pull request #4944 from wojas/one-dnsseckeeper-per-request

Fix API performance: one DNSSECKeeper per request

Merge pull request #4977 from rgacogne/more-nmg-unit-tests

Add more NetmaskGroup unit tests

Merge pull request #4963 from Habbie/dnsdist-doc-nit

fix some typos; improve argument references

Merge pull request #4972 from pieterlexis/root-dnssec

Add the 2017 root key

Merge pull request #4980 from Habbie/clarify

clarify checkbox comment

Merge pull request #4984 from rgacogne/rec-preout-remote

rec: Fix `remote`/`local` inversion in `preoutquery`

Merge pull request #4987 from rgacogne/dnsdist-prevent-caching-no-ttl

dnsdist: Don't cache answers without any TTL

dnsdist: Don't cache answers without any TTL

`RFC2308` states that "negative responses without SOA records SHOULD
NOT be cached as there is no way to prevent the negative responses
looping forever between a pair of servers even with a short TTL".

Use `${TRAVIS_BUILD_DIR}` instead of assuming the repo is in `pdns`

Thus avoiding issues when/if the repository is cloned with a different
name.

rec: Fix `remote`/`local` inversion in `preoutquery`

`dq.remoteaddr` should hold the authoritative server address, but
it was stored in `dq.localaddr` instead since
ba21fcfedc103f12b6a8eadc17f2797b6d7ffb7b.

dnsdist: Use `sendSizeAndMsgWithTimeout()` for TCP, Fast Open toward backends

Use `sendSizeAndMsgWithTimeout()` in Remote Logger (protobuf)

Add `sendSizeAndMsgWithTimeout()` to send size and data with a single call

clarify checkbox comment

Add more NetmaskGroup unit tests

* negative entries using the explicit flag
* IPv6 negative entries
* regular and negative entries from Netmask objects instead of strings

Add the 2017 root key

more assorted doc nits

typo

fix typo; improve argument references

Merge pull request #4967 from jsoref/spelling

Spelling

Merge pull request #4961 from rgacogne/tsig-canonical-algo

Lowercase the TSIG algorithm name in hash computation

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