Provides default changelog if no file is provided

Modules/CPackRPM.cmake

@@ -392,6 +392,8 @@ if(CPACK_RPM_CHANGELOG_FILE)
   else(EXISTS ${CPACK_RPM_CHANGELOG_FILE})
     message(SEND_ERROR "CPackRPM:Warning: CPACK_RPM_CHANGELOG_FILE <${CPACK_RPM_CHANGELOG_FILE}> does not exists - ignoring")
   endif(EXISTS ${CPACK_RPM_CHANGELOG_FILE})
+else(CPACK_RPM_CHANGELOG_FILE)
+  set(CPACK_RPM_SPEC_CHANGELOG "* Sun Jul 4 2010 Erk <[email protected]>\n  Generated by CPack RPM (no Changelog file were provided)")
 endif(CPACK_RPM_CHANGELOG_FILE)
 
 # CPACK_RPM_SPEC_MORE_DEFINE