Teach NarProperties to extract a list of all known AOLs

In the upcoming support for using native-lib-loader to unpack and load
our native libraries, we will need to stay platform-independent. Hence
we will need to know what native libraries are bundled for the current
architecture/OS. Unfortunately, this is not enough information because
NAR uses a full AOL identifier (in particular, the linker name) to
identify the location of the native library in the .nar file. To remedy
this, we will simply look in the paths corresponding to all AOLs
matching the current "AO".

Side note: using properties.keySet() does *not* work in NarProperties
because the properties are usually empty. The properties inherit their
defaults from an opaque Properties object passed to the constructor, hence
the keys we are after are only available via the propertyNames() method.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

src/main/java/com/github/maven_nar/NarProperties.java

@@ -21,10 +21,15 @@
 
 import java.io.File;
 import java.io.FileInputStream;
-import java.io.InputStream;
 import java.io.FileNotFoundException;
 import java.io.IOException;
+import java.io.InputStream;
+import java.util.Collection;
+import java.util.Enumeration;
+import java.util.LinkedHashSet;
 import java.util.Properties;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 import org.apache.maven.plugin.MojoFailureException;
 import org.apache.maven.project.MavenProject;
@@ -116,4 +121,20 @@ public static void inject(MavenProject project, InputStream properties) throws M
 	public String getProperty(String key) {
 		return properties.getProperty(key);
 	}
+
+	public Collection<String> getKnownAOLs() {
+		final Collection<String> result = new LinkedHashSet<String>();
+		final Pattern pattern = Pattern.compile("([^.]+)\\.([^.]+)\\.([^.]+).*");
+		final Enumeration<?> e = properties.propertyNames();
+		while (e.hasMoreElements()) {
+			final Object key = e.nextElement();
+			if (key instanceof String) {
+				final Matcher matcher = pattern.matcher((String) key);
+				if (matcher.matches()) {
+					result.add(matcher.group(1) + "-" + matcher.group(2) + "-" + matcher.group(3));
+				}
+			}
+		}
+		return result;
+	}
 }