RFR: Multiple minor fixes

[Roman Kennke]

Looks good!
Roman

> http://cr.openjdk.java.net/~shade/shenandoah/multi-1/webrev.01/
> 
> These are minor fixes that were sitting and rotting in my patch queue:
> 
>  *) The indenting in mark-compact code drives me nuts;
>  *) Full GC should acquire the heap lock once when starting to deal with regions;
>  *) Print "process weakrefs", to avoid confusion with coalesced UR;
>  *) Micro-optimize get_region
> 
> Testing: tier3_gc_shenandoah
> 
> Thanks,
> -Aleksey
>