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

[Erik Joelsson]

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/

/Erik