JDBM does not run on Android

[jankotek]

JDBM currently uses some private API from 'com.sun' package. This is needed for reasonable performance. We should provide an alternative to those API, so JDBM runs on Android.

Related compiler warnings:

[WARNING] /home/jan/IdeaProjects/JDBM3/src/main/java/net/kotek/jdbm/StorageDiskMapped.java:[3,15] sun.misc.Cleaner is Sun proprietary API and may be removed in a future release

[WARNING] /home/jan/IdeaProjects/JDBM3/src/main/java/net/kotek/jdbm/SerialClassInfo.java:[342,23] sun.reflect.ReflectionFactory is Sun proprietary API and may be removed in a future release

[WARNING] /home/jan/IdeaProjects/JDBM3/src/main/java/net/kotek/jdbm/SerialClassInfo.java:[343,31] sun.reflect.ReflectionFactory is Sun proprietary API and may be removed in a future release

[WARNING] /home/jan/IdeaProjects/JDBM3/src/main/java/net/kotek/jdbm/StorageDiskMapped.java:[118,12] sun.misc.Cleaner is Sun proprietary API and may be removed in a future release

[WARNING] /home/jan/IdeaProjects/JDBM3/src/main/java/net/kotek/jdbm/StorageDiskMapped.java:[118,42] sun.nio.ch.DirectBuffer is Sun proprietary API and may be removed in a future release

[jankotek]

Not going to fix in JDBM3, will address at JDBM4