Allow cross version tests to request that an isolated gradle user home dir be used.
Use an isolated user home dir for several cross version tests.
GRADLE-3153 - bump metadata cache version to avoid mismatch in cached ivy.xml namespace handling between Gradle 2.0 and 2.1+
Actually close the plugin resolution cache.

+review
Some javadoc updates.
Simplifications in ivy xml parser
Use correct cache version for 2.1-rc-2
Fixed broken int test for older gradle versions.
Force another test that compiles scala to fork the compiler when running with the daemon.

+review
Increase visibility of fixture to allow integ tests outside of scala project to apply it.

+review REVIEW-5175
Fixed using ivy repos in cross version tests for a few older Gradle versions.
Moved plugin development plugin to org.gradle.plugin.devel

+review REVIEW-4998
Revert "Moved plugin development plugin to org.gradle.plugin.devel"

We don't want any further changes in the release branch, and 'org.gradle.plugin.devel' is not the correct name for the package.
Fix for broken int test on unknown os.
Added Action override for AuthenticationSupported.credentials().
Declare the Action overrides for exec() and javaexec() on Script.
Method can be private.
Mark method as @Incubating.
Tweak to test.
Removed trace from int test.