Release Note: G1 May Uncommit Memory During Marking Cycle

By default, G1 may now give back Java heap memory to the operating system during any concurrent mark cycle. G1 will respect default Java heap sizing policies at that time.

This change improves memory usage of the Java process if the application does not need all memory.

This behavior may be disabled in accordance with default heap sizing policies by setting minimum Java heap size to maximum Java heap size via the `-Xms` option.