RFR: 8012564: The SOURCE value in release file of JDK 8 doesn't contain valid changesets for some OS since b74

[Tim Bell]

Erik:

> Simple patch removing unnecessary check for existence of mercurial for 
> getting the hgtips for the release file. This check prevented the 
> backup solution of using the .hgtip files from working when building 
> from source bundles.
>
> http://cr.openjdk.java.net/~erikj/8012564/webrev.root.01

Looks good.

Tim