RFR: 8234835 Use UTF-8 charset in make support Java code

[Dan Smith]

Please review this patch to make explicit use of the UTF-8 charset in build tools' IO code.

JDK-8065704 changed the platform default to US-ASCII, so the intended effect of this change is to address a regression and restore the typical earlier behavior.

My particular interest is in fixuppandoc, but it seems like we might has well patch all of this code to avoid relying on the platform default.

http://cr.openjdk.java.net/~dlsmith/8234835/