JDK-8136771: Implement the license-swap logic as a make target

[Tim Bell]

Erik:

> This is the open part of a larger Oracle internal change. I've 
> reimplemented how the .hgtip files are created. Now these can be 
> generated with only open source present. This is nice to have if you 
> create a source bundle and want to keep the information about where in 
> the HG history that source came from. There is also a minor build 
> bugfix in GensrcModuleInfo.gmk for when building with prebuilt crypto 
> binaries.
>
> Bugs: https://bugs.openjdk.java.net/browse/JDK-8136771
> Webrev: http://cr.openjdk.java.net/~erikj/8136771/webrev.top.01/

Looks good to me.

/Tim