ECPG: Move allocating struct statement earlier in ECPGdo().
ECPG: Move char *oldlocale from ECPGdo() to struct statement.
ECPG: Introduce ecpg_do_epilogue() to restore LC_NUMERIC and
      free the statement structure.
ECPG: Introduce ecpg_do(). The core function of ECPGdo() is
      separated out, so:
      - va_start and va_end are done centrally, and
      - it can be used elsewhere
ECPG: Simplify free_variable()
ECPG: Rename free_params() to ecpg_free_params(), make it public.
      Modify the ecpg_log() message in this function to reflect
      its new name. Some regression tests results have changed
      as a consequence.
      Move the nParams and paramValues variables from ecpg_execute
      to struct statement.