GXemul Code2

Updating ULTRIX installation instructions with ifconfig and route commands, for testing IPv4.

Minor stuff.

The fix 2018-06-13 for translation invalidation when using larger than 4 KB pages, which made HelenOS/malta run further, caused a regressions which broke NetBSD/hpcmips (on VR4121 CPUs, which have 1 KB native page size). A bit of cleanup seems to have fixed this, so that both NetBSD/hpcmips and HelenOS/malta work now.

PAGEMASK hack for VR41*

Nicer release notes.

Adding detection of /opt/X11/{include,lib} in the configure script, to build with X11 on MacOS with XQuartz installed (thanks to eschatologist in the #GXemul IRC channel on FreeNode for noticing this).

Removing guestoses.html.

Moving remaining modes from unsupported.html into individual machine pages, so that unsupported.html can be removed.

Removing the SGI IP30 and IP32 modes from the new framework; SGI machines are emulated using the old framework.

The guestoses.html page is almost gone.