Use unique_xmalloc_ptr for mi_parse::command

This changes mi_parse::command to be a unique_xmalloc_ptr and fixes up
all the uses.  This avoids some manual memory management.  std::string
is not used here due to how the Python API works -- this approach
avoids an extra copy there.

Reviewed-by: Keith Seitz <keiths@redhat.com>
5 files changed