Make cmake properly disable fortran upon user requirments

--- ./CMakeLists.txt.orig	2016-07-01 15:28:57.139304608 +0300
+++ ./CMakeLists.txt	2016-07-01 15:34:22.295899455 +0300
@@ -8,10 +8,13 @@
 
 INCLUDE(CheckLanguage)
 CHECK_LANGUAGE(Fortran)
-IF(CMAKE_Fortran_COMPILER)
+OPTION (MEDFILE_BUILD_FORTRAN "Build fortran library" ON)
+IF(MEDFILE_BUILD_FORTRAN)
   ENABLE_LANGUAGE(Fortran)
+  IF(NOT CMAKE_Fortran_COMPILER)
+      MESSAGE(FATAL_EROOR "Fortran support was requested but not found")
+  ENDIF()
 ELSE()
-  MESSAGE(STATUS "No Fortran support")
 ENDIF()
 
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