Users of the parse_options_concat() API function need to allocate
extra slots in advance and fill them with OPT_END() when they want
to decide the set of supported options dynamically, which makes the
code error-prone and hard to read.  This has been corrected by tweaking
the API to allocate and return a new copy of "struct option" array.

* jk/parse-options-concat:
  parse_options: allocate a new array when concatenating