CONFIG: adjustments to environment

- provide default WM_DIR if not already set, to improve robustness if a
  reduced environment is used

- add etc/ to WM_PROJECT_SITE search. This makes the site directory
  structure consistent with the OpenFOAM structure.
  Eg,

      WM_PROJECT_SITE/etc/..
      WM_PROJECT_SITE/bin/..
      WM_PROJECT_SITE/platforms/..

- Don't set/export WM_OSTYPE.  The default is POSIX and is properly
  defaulted throughout, including in CMakeLists-OpenFOAM.txt (also for
  Catalyst)

etc/config.sh/settings

@@ -18,7 +18,7 @@
 #
 #------------------------------------------------------------------------------
 export WM_ARCH=$(uname -s)                  # System name
-: ${WM_OSTYPE:=POSIX}; export WM_OSTYPE     # System type (POSIX is default)
+## : ${WM_OSTYPE:=POSIX}; export WM_OSTYPE     # System type (POSIX is default)
 
 # Default compiler = gcc/g++ and C++11
 export WM_CC="gcc"
@@ -167,7 +167,17 @@ export FOAM_USER_LIBBIN="$WM_PROJECT_USER_DIR/platforms/$WM_OPTIONS/lib"
 
 
 # Prepend wmake to the path - not required for runtime-only environment
-[ -d "$WM_DIR" ] && PATH="$WM_DIR:$PATH"
+foundDir="$WM_PROJECT_DIR/wmake"
+if [ -d "$WM_DIR" ]
+then
+    foundDir="${WM_DIR}"
+fi
+if [ -d "$foundDir" ]
+then
+    PATH="$foundDir:$PATH"
+else
+    unset WM_DIR
+fi
 
 # Prepend OpenFOAM scripts to the path
 export PATH="$WM_PROJECT_DIR/bin:$PATH"
@@ -336,7 +346,7 @@ esac
 
 # Cleanup
 # ~~~~~~~
-unset archDir siteDir
+unset archDir siteDir foundDir
 unset gcc_version gccDir
 unset gmp_version gmpDir  mpfr_version mpfrDir  mpc_version mpcDir
 unset clang_version clangDir