[perl #124628] [JVM] doesn't know about signals

[Pepe Schwarz via RT]

NQP commit d54d719311 and Rakudo commit 1acf805b6 add a workaround for the lack 
of actual signal handling on the JVM. Note this is for now limited to SIGINT 
and SIGKILL, and cannot work for any signal that doesn't want the receiving 
process to exit.