Trying to improve x49gp

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Today I participated in a discussion about 50G grayscale graphics on the Omnimaga forums. As a result of that, I wrote and posted a patch allowing the good old x49gp emulator to switch its display into grayscale mode. Then I got a message from debrouxl pushing me to post about that here so it doesn't get lost over there - only a few 50G owners are visiting Omnimaga. He has a point there ...

So here I am, a new MoHPC user (though I've read the forums for a few months now). A 50G is my only working HP calculator. I've learned that trying to write native ARM software for it is quite a hassle, especially if it uses grayscale, because there are not many emulation / debugging environments to choose from - either real hardware, putting my precious SysRPL projects in port 1 at risk of being deleted by buggy programs, or x49gp with its limitations. The discussion on Omnimaga motivated me to get rid of one limitation.
May it help someone else out there too. I'm sure I'll use it myself.

x49gp had some compilation problems on my system, I've patched the Makefile to work around them, and somewhen I found a typo in flash.c and fixed it. These fixes are bundled in another patch. Feedback is welcome, x49gp could become a 50G developer's friend if someone takes care of its problems, of which it probably has accumulated many over the years without maintenance in addition to those present from the beginning, like use of deprecated GTK2 functions.

... Why are diffs not an allowed attachment file type? Also, if this is posted in the wrong place, feel free to move it.