Small fix to configure.in in CVS

[Martin Ebourne]

Hi,

Fixes current CVS configure.in to refer to the right variable when  
doing the scary macro undefining stuff.

Cheers,

Martin.

--- emacs/configure.in~ 2006-09-28 06:47:26.000000000 +0100
+++ emacs/configure.in  2006-10-25 13:50:29.000000000 +0100
@@ -3230,7 +3230,7 @@
 # the C preprocessor to some helpful value like 1, or maybe the empty
 # string.  Needless to say consequent macro substitutions are less
 # than conducive to the makefile finding the correct directory.
-[undefs="`echo $top_srcdir $configuration $canonical |
+[undefs="`echo $ac_top_srcdir $configuration $canonical |
 sed -e 's/[^a-zA-Z0-9_]/ /g' -e 's/^/ /' -e 's/  *$//' \
     -e 's/  */ -U/g' -e 's/-U[0-9][^ ]*//g' \
 `"]