review Add a new warning in verifySourceClasspath

[surli]

This PR aims at avoiding issues like #1933

[pvojtechovsky]

Let's improve the javadoc too. Actually there is

	/**
	 * Sets the source class path of the Spoon model.
	 * After the class path is set, it can be retrieved by
	 * {@link #getSourceClasspath()}. Only .jar files or directories
	 * are accepted.
	 *
	 * @throws InvalidClassPathException if a given classpath does not exists or
	 * does not have the right format (.jar file or directory)
	 */
	void setSourceClasspath(String[] sourceClasspath);

Let's replace

Only .jar files or directories are accepted.

by: Only .jar files or directories with *.java files are accepted. The directories with *.jar files or *.class files are ignored.

Or may be we should automatically replace classpath which point to a directory by list of contained jar files? ... looks like clients expects .that .. and the java doc would be easier too...

WDYT?

[surli]

by: Only .jar files or directories with *.java files are accepted. The directories with *.jar files or *.class files are ignored.

I changed a bit the text:
Only .jar files or directories with *.class files are accepted. The *.jar or *.java files contained in given directories are ignored.

Or may be we should automatically replace classpath which point to a directory by list of contained jar files? ... looks like clients expects .that .. and the java doc would be easier too...

I though about that but it could be quite expensive: in #1933 the user tried to add its complete .m2 directory as sourceClasspath...