[syslinux] Some patches from mageia

[Erwan Velu]

Hi folks,

As per Ady request (thanks for the reminder), I forgot to send the patches
I run in Mageia.

There is two of them :

One is making errors in parsing modules.alias not fatal.

The other one is adding an option to chain to avoid reading garbage on the
command line.
I had some issues with gfxboot and had to implement that. I know it's a
workaround, I don't really get if that's useful for others. You can forget
it if you consider it as too weird.

You can get the two commits from my mageia_fixes branch here :
https://github.com/ErwanAliasr1/syslinux/tree/mageia-fixes

It's currently rebased on the current master.

Cheers,
Erwan