Unary + appends zero to lists.

Example:

  acid: +{}
  {0x00000000}

  acid: +{1}
  {0x00000001, 0x00000000}

  acid: defn x() { return {1} ; }
  acid: +x()
  {0x00000001, 0x00000000}

Cause:

  The parser converts '+x' to 'x+0'.  Such is reasonable for
  numeric arguments and has no effect on strings.  Unfortunately
  for lists, it results in a zero being appended.

This patch:

  The parser converts '+x' to 'x+ZN' and oadd() handles the ZN
  rhs when the expression is evaluated.

Patched:

  acid: +{}

  acid: +{1}
  {0x00000001}

  acid: defn x() { return {1} ; }
  acid: +x()
  {0x00000001}