Need reviewer - get_source.sh changes

[Kelly O'Hair]

This change does not impact any openjdk use, but helps the Oracle engineers get off the
forest extension (fclone command) if they want to.

Changes the get_source.sh script so that you can provide an optional server replacement
path for http://hg.openjdk.java.net and fetching the so called "closed" repositories.

7167593: Changed get_source.sh to allow for getting full oracle jdk repo forest
http://cr.openjdk.java.net/~ohair/openjdk8/get_source/webrev/

-kto