Make "." be the CLI's default classpath

Previously, the default classpath was empty. Now, in the absence of the
user providing a classpath via the -cp option, the default classpath
will be ".". If the user does specify a classpath, the classpath that's
used will be exactly what they have specified, i.e. "." will no longer
be on the classpath unless specified by the user.

The app sample integration test has been updated to verify that "." is
only the classpath by default.

Fixes #115

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/ScriptCommand.java

@@ -276,7 +276,7 @@ public class ScriptCommand implements Command {
 
 		@Override
 		public String[] getClasspath() {
-			return NO_CLASSPATH;
+			return DEFAULT_CLASSPATH;
 		}
 
 		@Override

spring-boot-cli/src/main/java/org/springframework/boot/cli/compiler/GroovyCompilerConfiguration.java

@@ -31,7 +31,7 @@ public interface GroovyCompilerConfiguration {
 	/**
 	 * Constant to be used when there is no {@link #getClasspath() classpath}.
 	 */
-	public static final String[] NO_CLASSPATH = {};
+	public static final String[] DEFAULT_CLASSPATH = { "." };
 
 	/**
 	 * Returns the scope in which the compiler operates.

spring-boot-cli/src/main/java/org/springframework/boot/cli/compiler/GroovyCompilerConfigurationAdapter.java

@@ -82,7 +82,7 @@ public class GroovyCompilerConfigurationAdapter implements GroovyCompilerConfigu
 		if (this.options.has(classpathOption)) {
 			return this.options.valueOf(classpathOption).split(":");
 		}
-		return NO_CLASSPATH;
+		return DEFAULT_CLASSPATH;
 	}
 
 	@Override