RFR: 8013552: Add build support for different man pages for OpenJDK and OracleJDK

[Tim Bell]

Erik:

> Open part of this review:
>
> The docs team will start producing separate man pages for openjdk and 
> oraclejdk. Here are the necessary changes to the makefiles to support 
> this. This was already done for 7u, but these are the changes for 8.
>
> http://cr.openjdk.java.net/~erikj/8013552/webrev.jdk.01

Looks good.

Tim