jar --create should create missing parent directories

Make "jar --create --file a/b/foo.jar" create missing parent directories a/b before writing to file "foo.jar" in directory "a/b".

This eliminates the need to create the destination directory "manually", for example calling an OS command "mkdir a/b" before the "jar" shown above.

Prior art: tools like "javac" and "javadoc" already do create missing parent directories before writing results into a designated destination directory passed via their `-d` option.