allow explicit spec of OCC libs

CMakeLists.txt

@@ -1102,6 +1102,10 @@ if(ENABLE_OCC)
       # TKAdvTools -- not necessary? (and removed from OCC 6.8)
       TKMath TKernel)
   list(LENGTH OCC_LIBS_REQUIRED NUM_OCC_LIBS_REQUIRED)
+  if(OCC_LIBS)
+    message(STATUS "OCC libraries specified explicitly: " ${OCC_LIBS})
+    list(LENGTH OCC_LIBS_REQUIRED NUM_OCC_LIBS)
+  else(OCC_LIBS)
     set(OCC_LIBS)
     foreach(OCC ${OCC_LIBS_REQUIRED})
       find_library(OCC_LIB ${OCC} HINTS ENV CASROOT PATH_SUFFIXES lib
@@ -1114,6 +1118,7 @@ if(ENABLE_OCC)
       unset(OCC_LIB CACHE)
     endforeach(OCC)
     list(LENGTH OCC_LIBS NUM_OCC_LIBS)
+  endif(OCC_LIBS)      
   if(NUM_OCC_LIBS EQUAL NUM_OCC_LIBS_REQUIRED)
     find_path(OCC_INC "BRep_Tool.hxx" PATHS ENV CASROOT PATH_SUFFIXES inc
               include include/oce opencascade)