texi2dvi: fix --build=clean

[Emanuele Giaquinta]

Hi,

revision 7144 introduced a bug in texi2dvi that causes the aux dir to
not be cleaned in --build=clean mode. The attached patch fixes it.

Emanuele

Index: texi2dvi
===================================================================
--- texi2dvi	(revision 7318)
+++ texi2dvi	(working copy)
@@ -1677,7 +1677,7 @@
 cleanup ()
 {
   case $clean:$tidy in
-    true:false) mostly_clean ;;               # build mode is "clean"
+    true:true) mostly_clean ;;                # build mode is "clean"
     false:false) cd_orig; remove "$t2ddir";;  # build mode is "local"
   esac
 }