Rename ring binary to ring.cx

On some Linux distribution, /usr/bin/ring is already used by the
`alliance` package. Therefore we are renaming it to /usr/bin/ring.cx
to avoid conflicts.

Change-Id: I3f6e1667e6093eb5cd154a17ef040e6836388d2a
Tuleap: #598
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 71a221a..fc0f4b1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -413,7 +413,7 @@
 # install shell script which will launch "ring"
 INSTALL(
    FILES
-      "${PROJECT_SOURCE_DIR}/src/ring"
+      "${PROJECT_SOURCE_DIR}/src/ring.cx"
    DESTINATION
       ${CMAKE_INSTALL_PREFIX}/bin
    PERMISSIONS