RFR: 8141496: BitMap set operations copy their other BitMap argument

[Stefan Karlsson]

Hi all,

Please review this patch to make the BitMap operations take const BitMap 
references instead of copying the BitMaps.

http://cr.openjdk.java.net/~stefank/8141496/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8141496

The patch is needed in preparation for:
  https://bugs.openjdk.java.net/browse/JDK-8141501
  Problems with BitMap buffer management

Tested in JPRT (together with prototypes for JDK-8141501).

Thanks,
StefanK