Remove some rendundant Javadoc markup, and tweak some spacing.
Add note on how Gradle.getGradleHome() can return a surprising value when using the daemon to the Javadoc.
Don't run performance tests by adding it to the list of excluded tasks.
Revert "Allow build types to mess with the StartParameter as part of their definition."

This reverts commit 28ca090d5ce8dce8053c3901073a5fac55d35905.
Only consider IO exceptions as indicating that the release notes data feeds are unavailable and therefore the tests should be ignored.
Allow tests to specify GRADLE_OPTS env var values.
Don't quote the jvm args the daemon adds in case one with a space is added later.
Instead of dropping JVM args with spaces in them where they aren't supported (i.e. old versions), error instead.
Move setting of -Dfile.encoding to the base executer.
Let CollectionUtils.sort() accept an iterable.

Also added some unit tests.
Be explicit about the test kit defaulting to whatever Gradle runtime the tooling api selects by default.
Change GradleRunner API to have explicit succeeds() / fails() methods instead of an unopinionated run() method.
Change getGradleUserHomeDir() to return TestFile.