Update copyright dates for 2013.

On generated files in git and README.
Refresh README file.
java: Tidy up javadoc.
java: Change synopsis in man page to show use of add_drive.
java: Use defined constants for flags in call to guestfs_create_flags.
java: Implement the event API.
podwrapper: Refresh podwrapper man page.

This also adds a rule so you can do:

 make podwrapper.1

if you want to read the documentation as a man page.