CONFIG: address differences between shells

- suppress error messages that appear with zsh.
  According to unset(1p), 'unset -f' unsets a function.
  If the function was not previously defined, this is a no-op.
  This is similar for zsh, but there it emits a warning if the
  function was not previously defined.

- avoid 'local' in functions sources from etc/bashrc.
  ksh does not support this.

- use 'command' shell builtin instead of 'type'.
  Seems to be more consistent between shell flavours.

wmake/scripts/cmakeFunctions

@@ -158,7 +158,7 @@ canBuildPlugin()
         return 1
     }
 
-    type cmake > /dev/null 2>&1 || {
+    command -v cmake > /dev/null 2>&1 || {
         echo "==> cannot build ParaView plugins without cmake"
         return 1
     }