rpm: code shrink. Now uses open_zipped's logic (factored out into setup_unzip_on_fd())

function                                             old     new   delta
setup_unzip_on_fd                                      -      80     +80
open_zipped                                          176     113     -63
rpm_main                                            1672    1355    -317
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 0/2 up/down: 80/-380)          Total: -300 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/include/libbb.h b/include/libbb.h
index 976120e..2f67c7f 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -651,6 +651,15 @@
 extern void *xmalloc_read(int fd, size_t *maxsz_p) FAST_FUNC RETURNS_MALLOC;
 /* Returns NULL if file can't be opened (default max size: INT_MAX - 4095) */
 extern void *xmalloc_open_read_close(const char *filename, size_t *maxsz_p) FAST_FUNC RETURNS_MALLOC;
+/* Autodetects gzip/bzip2 formats. fd may be in the middle of the file! */
+#if ENABLE_FEATURE_SEAMLESS_LZMA \
+ || ENABLE_FEATURE_SEAMLESS_BZ2 \
+ || ENABLE_FEATURE_SEAMLESS_GZ \
+ /* || ENABLE_FEATURE_SEAMLESS_Z */
+extern int setup_unzip_on_fd(int fd /*, int fail_if_not_detected*/) FAST_FUNC;
+#else
+# define setup_unzip_on_fd(...) ((void)0)
+#endif
 /* Autodetects .gz etc */
 extern int open_zipped(const char *fname) FAST_FUNC;
 extern void *xmalloc_open_zipped_read_close(const char *fname, size_t *maxsz_p) FAST_FUNC RETURNS_MALLOC;