RFR: 8229838: Rename markOop files to markWord

[Stefan Karlsson]

Hi all,

Please review this patch to rename the markOop files to markWord.

http://cr.openjdk.java.net/~stefank/8229838/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8229838

JDK-8229258 reworked and renamed the markOopDesc class and markOop 
typedef, but the rename of the files were deferred. This patch renames 
the files to match the new name.

Thanks,
StefanK