Throw exception for minimal AJC runtime version violation

When running AJC, throw an AbortException(MINIMAL_JRE_VERSION) instead
of just logging an error, if the minimal JRE version requirement is
violated. Otherwise, in-process compilation would not fail due to the
skipped System.exit(-1) that was used before. In-process compilation is,
for example, relevant for AspectJ Maven Plugin, but also for non-forked
executions of Plexus AspectJ via Maven Compiler.

I am not 100% sure that AbortException is the appropriate exception
type, because it was designed for an aborted compilation process and
here compilation has not even started yet, but it seems to work fine.

Relates to #269.
Fixes #292.

Signed-off-by: Alexander Kriegisch <Alexander@Kriegisch.name>

org.aspectj.ajdt.core/src/main/java/org/aspectj/tools/ajc/Main.java

@@ -244,12 +244,8 @@ public class Main {
 		// will see ugly UnsupportedClassVersionError stack traces, which they might or might not interpret correctly.
 		// Therefore, interrupt AJC usage right here, even if it means that not even a usage page can be printed. It is
 		// better to save users from subsequent problems later.
-		if (SourceVersion.latest().ordinal() < MINIMAL_JRE_VERSION) {
-			System.err.println(MINIMAL_JRE_VERSION_ERROR);
-			if (doExit)
-				System.exit(-1);
-			return;
-		}
+		if (SourceVersion.latest().ordinal() < MINIMAL_JRE_VERSION)
+			throw new AbortException(MINIMAL_JRE_VERSION_ERROR);
 
 		// Urk - default no check for AJDT, enabled here for Ant, command-line
 		AjBuildManager.enableRuntimeVersionCheck(this);