[PATCH] Add a gzip fastpath for the xmalloc readers, v3

[Denys Vlasenko]

Please see attached patch (only compile-tested so far).
It builds on your work, implementing in-memory compression
for all unpackers we have.

Unfortunately, bloatcheck is not inspiring:

function                                             old     new   delta
transformer_write                                      -     133    +133
setup_transformer_on_fd                                -     133    +133
complete_cmd_dir_file                                773     895    +122
open_transformer_state                                 -      92     +92
xmalloc_open_zipped_read_close                        63     112     +49
xtransformer_write                                     -      24     +24
unpack_lzma_stream                                  2717    2737     +20
unpack_xz_stream                                    2393    2407     +14
unpack_Z_stream                                     1173    1183     +10
unpack_gz_stream                                     693     696      +3
decode_one_format                                    726     729      +3
refresh                                              665     667      +2
inflate_unzip                                        111     113      +2
unpack_bz2_stream                                    359     360      +1
swap_on_off_main                                     420     418      -2
scan_recursive                                       380     378      -2
inflate_unzip_internal                              1945    1924     -21
open_zipped                                           89      47     -42
setup_unzip_on_fd                                    142      53     -89
------------------------------------------------------------------------------
(add/remove: 4/0 grow/shrink: 10/5 up/down: 608/-156)         Total: 452 bytes
   text    data     bss     dec     hex filename
 923218     928   17684  941830   e5f06 busybox_old
 923686     928   17684  942298   e60da busybox_unstripped