Groovyc Ant task hard-codes

The ant task for Groovy hard-codes the glob pattern "*.groovy" when searching for source files. This obviously doesn't work for those of us who use a different extension (like ".g"). I've attached a patch that adds a property called "scriptExtension" to the task, which parallels GMaven's defaultScriptExtension property. This makes the extension configurable. It defaults to ".groovy" but can be changed if one uses something different.