Add a Conflicts: with weston, so that we can't try to install both

Change-Id: I704a5205c57ca3a175b527e97a34b1a0d3d8fb2f
diff --git a/debian/control b/debian/control
index c01384b..76d488d 100644
--- a/debian/control
+++ b/debian/control
@@ -49,4 +49,5 @@
  ${misc:Depends}
 Multi-Arch: foreign
 Provides: weston
+Conflicts: weston
 Description: Weston compositor w/ IMX support.