Fix #1181: Support supplementary chars in RuntimeString.
Merge pull request #1270 from sjrd/fix-supplem-chars-in-runtimestring

Fix #1181: Support supplementary chars in RuntimeString.
Fix #1236: Implement java.io.PrintWriter.
Merge pull request #1273 from sjrd/printwriter

Fix #1236: Implement java.io.PrintWriter.
Implement part of java.nio.{Byte,Char}Buffer.

These are required to implement Charset encoders and decoders.