Recognize `.nix' files as text files.
--- idutils-4.5/libidu/id-lang.map 2009-05-17 16:38:42.000000000 +0200
+++ idutils-4.5/libidu/id-lang.map 2010-07-04 15:52:48.000000000 +0200
@@ -88,6 +88,7 @@ GNUmakefile make
*.doc text
*.txt text
*.org text
+*.nix text
*.m4 m4
*.ac m4