ENH: Superbuild - Underscore are now valid character in CTK library option name

CMake/ctkFunctionExtractOptionNameAndValue.cmake

@@ -6,7 +6,7 @@
 FUNCTION(ctkFunctionExtractOptionNameAndValue my_opt var_opt_name var_opt_value)
 
  # Make sure option is correctly formated
-  IF(NOT "${my_opt}" MATCHES "^[/A-Za-z0-9.]+:(ON|OFF)")
+  IF(NOT "${my_opt}" MATCHES "^[/A-Za-z0-9._]+:(ON|OFF)")
     MESSAGE(FATAL_ERROR "Option ${my_opt} is incorrect. Options should be specified using the following format OPT1:[ON|OFF]. For example OPT1:OFF or OPT2:ON")
   ENDIF()