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.

etc/config.sh/paraview

@@ -173,7 +173,7 @@ unset -f _foamParaviewEval
 unset cleaned cmake cmake_version pvName pvMajor pvLibDir pvPython
 unset ParaView_MAJOR
 
-if type _foamAddLib > /dev/null 2>&1    # normal sourcing
+if command -v _foamAddLib > /dev/null 2>&1  # normal sourcing
 then
     unset ParaView_VERSION
 fi