Backport from trunk
        PR libgfortran/65089
        * io/format.h (free_format): New function to free memory
        allocated for building format error messages.
        * io/format.c (format_error): Add checks before freeing memory
        to avoid potential segfaults and free formatting data when
        needed on error conditions. Always allocate and NULL terminate
        the string.
        * io/transfer.c (st_read_done, st_write_done): Use new
        free_format function to clean up memory allocations when done.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-5-branch@229935 138bc75d-0d04-0410-961f-82ee72b054a4