Always write temporary projects for non-Maven sources

When compiling a .java file that is contained in, say, a Downloads/
directory, we definitely do not want to compile all of the .java files
available in the complete Downloads/** directory structure.

Now, we could special-case .java files containing the source for a class
in the default package, while still trying to discover .java files
recursively when the class is in a package and the directory structure
agrees with the package name.

But that would just violate the Law of the Least Surprise and confuse
people. So let's just make a temporary project in *every* case where we
do not find a pom.xml file in the expected location.

Incidentally, this makes sure that we always include pom.xml files in
the generated .jar files.

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

Author: dscho

src/main/java/org/scijava/plugins/scripting/java/JavaEngine.java

@@ -296,9 +296,7 @@ private MavenProject getMavenProject(final BuildEnvironment env,
 			final File pom = new File(path, "pom.xml");
 			if (pom.exists()) return env.parse(pom, null);
 		}
-		final File rootDirectory = file.getParentFile();
-		final String artifactId = fakeArtifactId(env, file.getName());
-		return fakePOM(env, rootDirectory, artifactId, mainClass);
+		return writeTemporaryProject(env, new FileReader(file));
 	}
 
 	private static String getFullClassName(final File file) throws IOException {
@@ -405,7 +403,6 @@ private static MavenProject fakePOM(final BuildEnvironment env,
 		append(pom, project, "version", DEFAULT_VERSION);
 
 		final Element build = append(pom, project, "build", null);
-		append(pom, build, "sourceDirectory", directory.getPath());
 
 		if (mainClass != null) {
 			final Element plugins = append(pom, build, "plugins", null);