Update autogen.sh to support out-of-source build

.gitignore

@@ -10,6 +10,7 @@ Makefile.in
 aclocal.m4
 autom4te.cache/
 build-aux/
+build/
 config.h
 config.h.in
 config.h.in~

autogen.sh

@@ -1,8 +1,17 @@
 #!/bin/sh
 set -e
-mkdir -p m4
-autoreconf -i
 
-if test ! "x$NOCONFIGURE" = "x1" ; then
-    exec ./configure "$@"
+srcdir=`dirname $0`
+test -z "$srcdir" && srcdir=.
+
+origdir=`pwd`
+cd $srcdir
+
+mkdir -p m4
+autoreconf -is --force
+
+cd $origdir
+
+if test -z "$NOCONFIGURE" ; then
+    exec $srcdir/configure "$@"
 fi