SI-6532 emit debug info in compiled java.

Our handful of java source files weren't being compiled with line numbers,
sourcefile, and other debugger aids. I don't really know how to test this so
I'll enclose an excerpt of the bytecode diff of scala.runtime.IntRef to show
that this change results in debug information.

  2,3c2,4
 >   Compiled from "IntRef.java"
 4a6
 >   SourceFile: "IntRef.java"
 53a62,67
 >       LineNumberTable:
 >         line 18: 0
 >       LocalVariableTable:
 >         Start  Length  Slot  Name   Signature
 >                0      10     0  this   Lscala/runtime/IntRef;
 >                0      10     1  elem   I
 62a77,81
 >       LineNumberTable:
 >         line 19: 0
 >       LocalVariableTable:
 >         Start  Length  Slot  Name   Signature
 >                0       8     0  this   Lscala/runtime/IntRef;