Travis dangling symlinks

[jsoref]

Short description

Yak: recursor and dnsdist rely on symlinks into the 'main' pdns source tree. Travis should check for dangling symlinks.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[jsoref]

https://travis-ci.org/PowerDNS/pdns/jobs/437438861

cd pdns/recursordist
$ for a in $(find * -type l|egrep -v "pubsuffix.cc|missing-sources|so$"); do [ ! -e $a ] && echo found dangling symlink $a && exit 1; done
found dangling symlink no-such-file
The command "./build-scripts/travis.sh" exited with 1.
Done. Your build exited with 1.

[jsoref]

Here's the final tested version:

$ ! find -L . -name missing-sources -prune -o ! -name pubsuffix.cc -type l | grep .
./dangling-two
./dangling-one
The command "! find -L . -name missing-sources -prune -o ! -name pubsuffix.cc -type l | grep ." failed and exited with 1 during .
Your build has been stopped.

https://travis-ci.org/PowerDNS/pdns/jobs/438777874

[rgacogne]

rec is failing to build, rebasing on top of #7044 should fix it, sorry!