ENH: install scotch files under ThirdyParty platforms/

- for future updates of scotch, need to edit these two files:

    OpenFOAM-<VERSION>/src/parallel/decompose/Allwmake
    ThirdParty-<VERSION>/Allwmake

src/parallel/decompose/Allwmake

@@ -2,6 +2,10 @@
 cd ${0%/*} || exit 1    # run from this directory
 set -x
 
+SCOTCH_VERSION=scotch_5.1.10b
+SCOTCH_ARCH_PATH=$WM_THIRD_PARTY_DIR/platforms/$WM_ARCH$WM_COMPILER/$SCOTCH_VERSION
+export SCOTCH_ARCH_PATH
+
 wmakeLnInclude decompositionMethods
 
 wmake libso scotchDecomp
@@ -9,7 +13,10 @@ wmake libso metisDecomp
 
 if [ -d "$FOAM_MPI_LIBBIN" ]
 then
-    ( WM_OPTIONS=${WM_OPTIONS}$WM_MPLIB; wmake libso ptscotchDecomp )
+(
+    WM_OPTIONS=${WM_OPTIONS}$WM_MPLIB
+    wmake libso ptscotchDecomp
+)
 fi
 
 wmake libso decompositionMethods