Add a 'comparator' field to TreeMap

This will be needed for Java-compatible serialization of tree maps.

Note that the field should be null when the TreeMap uses the default
comparator.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make TreeMap (de)serialization compatible with Java

This is done by implementing the readObject()/writeObject() method
pair as demanded by the serialization specification. The specifics
were reverse-engineered from serializing trivial TreeMap instances
with OpenJDK.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Add a test to ensure TreeMap's (de)serialization compatibility with OpenJDK

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Make ArrayList's serialization compatible with OpenJDK's

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Mark java.lang.Number as serializable

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Serialize test: augment the hexdump with address and ASCII dump

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>