[bootstrap.mk] change configure.in -> configure.ac

Fix warnings during compile, that configure.in is
deprecated.

bootstrap.mk

@@ -1,6 +1,6 @@
-BOOTSTRAP_SUBDIRS += configure.in
+BOOTSTRAP_SUBDIRS += configure.ac
 BOOTSTRAP_SUBDIRS += xbmc/screensavers/rsxs-0.9/configure.ac
-BOOTSTRAP_SUBDIRS += xbmc/visualizations/Goom/goom2k4-0/configure.in
+BOOTSTRAP_SUBDIRS += xbmc/visualizations/Goom/goom2k4-0/configure.ac
 BOOTSTRAP_SUBDIRS += lib/cpluff/configure.ac
 BOOTSTRAP_SUBDIRS += lib/gtest/configure.ac
 
@@ -30,7 +30,7 @@ lib/libdvd/libdvdnav/configure: lib/libdvd/libdvdread/configure
 	autoreconf -vif $(@D)
 	-@rm -rf $(@D)/autom4te.cache
 
-configure: configure.in
+configure: configure.ac
 	autoreconf -vif $(@D)
 	-@rm -rf $(@D)/autom4te.cache
 	@test -n "$$BOOTSTRAP_STANDALONE" || ( echo "Configuration is stale. You should almost certainly reconfigure" && false )