#41 Supporting OpenJdk 21

[Pierre Gruet]

Hello,

In Debian, we are getting ready to switch to OpenJDK-21 in a somewhat near future. Jmol is almost compliant, we just saw that the return type of Lst.addLast() conflicts with the one of List.addLast(), which is introduced in OpenJDK-21. Changing the return type and removing the "return" like in the enclosed patch solves the issue and allows one to build Jmol with OpenJDK-17 and OpenJDK-21.

Best,

--
Pierre