cmake: softer handling of Sparkle

emit a warning instead of a fatal error when Sparkle framework is
not found

Change-Id: Iccffaa3047ba2b37813b33e920f5b311b74db5b8
Tuleap: #449

CMakeLists.txt

@@ -53,7 +53,8 @@ IF(NOT (${ENABLE_SPARKLE} MATCHES false))
          MESSAGE(WARNING "${PUBLIC_KEY_PATH} not found Sparkle Framework will NOT work and may even prevent application from launching. Please consider disabling Sparkle Framework, creating a keypair for testing purposes")
       ENDIF(EXISTS ${PUBLIC_KEY_PATH})
    ELSE()
-      MESSAGE(FATAL_ERROR "Sparkle framework not found, build it (see README) or disable Sparkle (-DENABLE_SPARKLE=false)")
+      MESSAGE(WARNING "Sparkle framework not found, disabling it... to build it see README")
+      SET(ENABLE_SPARKLE 0 CACHE BOOLEAN "Enable Sparkle")
    ENDIF(EXISTS ${SPARKLE_FRAMEWORK})
 ENDIF(NOT (${ENABLE_SPARKLE} MATCHES false))