Clarify classpath vs. gosuClasspath in DefaultGosuCompileSpec and AntGosuCompile

[DPUkyle]

Other JVM language plugins keep a classpath argument, and a groovyClasspath/scalaClasspath too - both are FileCollections.

The Gosu plugin (as of 0.1.2-alpha) is confusing in its misuse of these parameters.

To clarify:

• classpath should be exactly what it sounds like - it should contain the explicitly declared compile-time dependencies and their transitive dependencies
• gosuClasspath should contain only the additional inferred Gosu jar: gosu-ant-compiler and its transitive runtime dependency on gosu-core.

Finally, before creating a new ant process we will typically concatenate these two FileCollections. Ensure that gosuClasspath is added last, in case (for some reason) a different gosu-core jar is already added to classpath; first one wins with classpath resolution and appending gosuClasspath, rather than pre-pending, should preserve this behavior.

[DPUkyle]

This is fixed; before launching the AntBuilder we create a jointClasspath, which has some duplicated values. It might be worth de-duping this List at some point in the future, though there should be no functional change - it's purely cosmetic and would make debugging output easier to read.