RFR: Backout: Refactor evac-in-progress flag to more general gc-phase flag

[Roman Kennke]

This is a clean backout of the previous change "Refactor 
evac-in-progress flag to more general gc-phase flag". In discussions we 
came to the conclusion that we should leave that code as it was, and 
instead make new experimental code check for existing flags.

Ok to back out that change?

http://cr.openjdk.java.net/~rkennke/backout-gcflags/webrev.00/ 
<http://cr.openjdk.java.net/%7Erkennke/backout-gcflags/webrev.00/>

Roman