RFR: 8025796: (s) hgforest.sh could trigger unbuffered output from hg without complicated machinations

[Mike Duigou]

Hello all;

This changeset provides hgforest.sh a more consistent mechanism for ensuring that the mercurial python instance produces unbuffered output (for timely status). The technique used was suggested by Dmitry Samersoff and seems to work on all platforms that I have tested it; linux, macos and solaris. I have yet to test it on windows/cygwin but want to get other user's reports to determine if this is a viable direction. 

The changeset:

http://cr.openjdk.java.net/~mduigou/JDK-8025796/0/webrev/

Thanks,

Mike