Also add minidns-core as dependency to smack-core. This requires
increasing the minimum required Android SDK level to 9, as this is
what MiniDNS requires.
In dd84d53bbc the usage of dynamic
dependencies was removed because OSS Sonatype would not longer allow
them, i.e. the '1.2.+' notation, on release artifacts. But they allow
the mathematical range notation '(1.2,1.3]', therefore we use this now.