Adds tasks that check that the all jars that we build have LICENSE.txt
and NOTICE.txt files and that the files are correct. Sets check to
depend on these task.
This is mostly there for extra parnoia because we automatically
configure all Jar tasks to include the LICENSE.txt and NOTICE.txt
files anyway. But it is quite possible to add configuration to those
tasks that would override either file.
This causes check to depend on several more things than it used to.
Take, for example, javadoc:
check depends on the new verifyJavadocJarNotice which depends on
extractJavadocJar which depends on javadocJar which depends on
javadoc, this check now depends on javadoc.
a8f40b3e04