Added helpful error messages for erroneous arguments

import edg.slicing.ConstrainedAlgorithm;

import edg.slicing.SlicingAlgorithm;

import edg.slicing.SlicingCriterion;

import eknife.config.Config;

import java.io.File;

import java.util.LinkedList;

import java.util.List;

import java.util.Set;

public class EKnife

		help += "  -l,--line   <num>           The line of the slicing criterion\n";

		help += "  -v,--var    <name>          The name of the slicing criterion (must be a variable)\n";

		help += "  -n,--occurrence <num>       The occurrence of the slicing criterion in that line\n";

		help += "  -G --print-graph <file.dot> Exports the graph as a dot file\n";

		help += "  -G --print-graph <file.pdf> Exports the graph as a PDF file\n";

		help += "  -G,--print-graph <file.dot> Exports the graph as a dot file\n";

		help += "  -G,--print-graph <file.pdf> Exports the graph as a PDF file\n";

		help += "  --help                      Show this message.\n";

		System.out.print(help);

		}

		boolean isValid() {

			return inputPath != null && new File(inputPath).exists() &&

					outputFile != null && (outputFile.exists() || outputFile.getAbsoluteFile().getParentFile().isDirectory()) &&

					file != null &&

					line > 0 &&

					name != null && !name.isEmpty() &&

					occurrence > 0;

			List<String> errors = new LinkedList<>();

			if (inputPath == null)

				errors.add("You must specify a file to analyze with '-i'.");

			else if (!new File(inputPath).exists())

				errors.add("The input file you've specified does not exist or isn't readable(" + inputPath + ").");

			if (outputFile == null)

				errors.add("You must specify a location for the output with '-o'.");

			else if (!outputFile.exists() && !outputFile.getAbsoluteFile().getParentFile().isDirectory())

				errors.add("The output file's parent folder does not exist, or the output folder does not exist.");

			if (file == null)

				errors.add("The input file is a folder, so you must specify a the file that contains the slicing criterion with '-f'.");

			if (line <= 0)

				errors.add("You must specify a line number greater than 0 with '-l'.");

			if (name == null || name.isEmpty())

				errors.add("You must specify a valid variable name with '-v'.");

			if (occurrence <= 0)

				errors.add("You must specify an occurrence greater than 0 with '-n'.");

			for (String error : errors)

				System.out.println(error);

			return errors.isEmpty();

		}

	}

}