Please handle end-of-file gracefully

[Ingo60]

Example session, at prompt enter CTRL-D:

ingo@ibinti:~/repl$ java -jar frege-repl-1.0.3-SNAPSHOT.jar -warn -hints
Welcome to Frege 3.21.500-g88270a0 (Oracle Corporation OpenJDK Server VM, 1.7.0_51)

frege> Exception in thread "main" java.lang.NullPointerException
at frege.repl.FregeRepl$TCommand$M.parse(FregeRepl.java:3092)
at frege.repl.FregeRepl$17.eval(FregeRepl.java:5309)
at frege.repl.FregeRepl$17.eval(FregeRepl.java:5243)
at frege.runtime.Fun1$1.eval(Fun1.java:62)
at frege.runtime.Delayed.call(Delayed.java:198)
at frege.runtime.Delayed.forced(Delayed.java:267)
at frege.repl.FregeRepl$40.eval(FregeRepl.java:6390)
at frege.runtime.Fun1$1.eval(Fun1.java:62)
at frege.runtime.Delayed.call(Delayed.java:198)
at frege.runtime.Delayed.forced(Delayed.java:257)
at frege.repl.FregeRepl$41.eval(FregeRepl.java:6459)
at frege.runtime.Fun1$1.eval(Fun1.java:62)
at frege.runtime.Delayed.call(Delayed.java:198)
at frege.runtime.Runtime.runMain(Runtime.java:225)
at frege.repl.FregeRepl.main(FregeRepl.java:7182)