autogen.sh: open-code pushd/popd

This script uses /bin/sh, which on Debian-like systems is dash, which
does not support bash's pushd/popd.

autogen.sh

@@ -3,7 +3,8 @@
 srcdir=`dirname $0`
 test -z "$srcdir" && srcdir=.
 
-pushd $srcdir
+olddir=`pwd`
+cd "$srcdir"
 
 aclocal || exit 1
 autoheader || exit 1
@@ -13,7 +14,8 @@ intltoolize -c -f || exit 1
 libtoolize -c || exit 1
 autoconf || exit 1
 automake -a -c || exit 1
-popd
+
+cd "$olddir"
 
 if test -z "$NOCONFIGURE"; then
 	$srcdir/configure --enable-maintainer-mode $*