#35 strl.h has moved in latest libstrl

[starlight]

built 2.10.3 from source usng libstrl-0.5.1 and
found that the path for strl.h has changed

from
/usr/local/include/strl/strl.h
to
/usr/local/include/strl.h

patch included with this tickert

[Murray S. Kucherawy]

Fixed (slightly differently) for next release.

[Egbert S]

Apparently it's broken again.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=948504
https://sourceforge.net/p/opendkim/bugs/250/