Convert to do default find_packaage() but respond to std TriBITS TPL …

…vars (TriBITSPub#156)

This now matches the standard behavior defined in the TriBITS Developers
Guide.

The FIND_PACKAGE(CGNS) call was made optional as per the standard.  But that
should be okay because if that fails, then if the standard TriBITS TPL find
fails, then the TPL find will bomb out.

tribits/common_tpls/FindTPLCGNS.cmake

@@ -37,14 +37,45 @@
 # ************************************************************************
 # @HEADER
 
-SET(CMAKE_MODULE_PATH
-  "${CMAKE_MODULE_PATH}"
-  "${CMAKE_CURRENT_LIST_DIR}/find_modules"
-  "${CMAKE_CURRENT_LIST_DIR}/utils"
-   )
+#
+# First, set up the variables for the (backward-compatible) TriBITS way of
+# finding Netcdf.  These are used in case FIND_PACKAGE(NetCDF ...) is not
+# called or does not find NetCDF.  Also, these variables need to be non-null
+# in order to trigger the right behavior in the function
+# TRIBITS_TPL_FIND_INCLUDE_DIRS_AND_LIBRARIES().
+#
+SET(REQUIRED_HEADERS cgnslib.h)
+SET(REQUIRED_LIBS_NAMES cgns)
+
+#
+# Second, search for Netcdf components (if allowed) using the standard
+# FIND_PACKAGE(CGNS ...).
+#
+TRIBITS_TPL_ALLOW_PRE_FIND_PACKAGE(CGNS  CGNS_ALLOW_PREFIND)
+IF (CGNS_ALLOW_PREFIND)
 
-find_package(CGNS REQUIRED)
+  MESSAGE("-- Using FIND_PACKAGE(CGNS ...) ...")
 
+  SET(CMAKE_MODULE_PATH
+    "${CMAKE_MODULE_PATH}"
+    "${CMAKE_CURRENT_LIST_DIR}/find_modules"
+    "${CMAKE_CURRENT_LIST_DIR}/utils"
+     )
+
+  find_package(CGNS)
+
+  IF (CGNS_FOUND)
+    set(TPL_CGNS_LIBRARIES ${CGNS_LIBRARIES} CACHE PATH
+      "List of semi-colon seprated (full) paths to the CGNS libraries")
+    set(TPL_CGNS_INCLUDE_DIRS ${CGNS_INCLUDE_DIRS} CACHE PATH
+      "List of semi-colon seprated list of directories containing CGNS header files")
+  ENDIF()
+
+ENDIF()
+
+#
+# Third, call TRIBITS_TPL_FIND_INCLUDE_DIRS_AND_LIBRARIES()
+#
 TRIBITS_TPL_FIND_INCLUDE_DIRS_AND_LIBRARIES( CGNS
-  REQUIRED_HEADERS cgnslib.h
-  REQUIRED_LIBS_NAMES "cgns")
+  REQUIRED_HEADERS ${REQUIRED_HEADERS}
+  REQUIRED_LIBS_NAMES ${REQUIRED_LIBS_NAMES})