chkconfig.ltx: check for some XeTeX requirements

- iftex is necessary for XeTeX with non-Latin scripts
- xetex.def is a separate package on CTAN and necessary for XeTeX and colors and graphics

lib/chkconfig.ltx

@@ -314,6 +314,7 @@
 \TestPackage{graphicx}
 \TestPackage{hyperref}
 \TestPackage{hyphenat}
+\TestPackage{iftex}
 \TestPackage[japanese.ldf]{japanese}
 \TestPackage{jurabib}
 \TestPackage{latex8}
@@ -364,6 +365,7 @@
 \TestPackage{wrapfig}
 \TestPackage{xargs}
 \TestPackage{xcolor}
+\TestPackage[xetex.def]{xetex-def}
 \TestPackage{xkeyval}
 
 % Packages used by LyX's documentation files