* Add DNS-over-HTTPS support to (*Client).Exchange
* Ignore net/http goroutine leak from DoH
* Use existing Dialer and TLSConfig fields on Client for DOH
* Make DOH http.Client fully configurable
* Pipe context into exchangeDOH
* txt parser: fix goroutine leak
When a higher level (grammar or syntax) error was encountered the lower
level zlexer routine would be left open and trying to send more tokens
on the channel c. This leaks a goroutine, per failed parse...
This PR fixes this by signalling this error - by canceling a context -
retrieving any remaining items from the channel, so zlexer can return.
It also adds a goroutine leak test that can be re-used in other tests,
the TestParseBadNAPTR test uses this leak detector.
The private key parsing code had the same bug and is also fixed in this
PR.
Fixes#586
Fixes https://github.com/coredns/coredns/issues/1233
* sem not needed anymore
Tom Thorogood
Miek Gieben