lib/transaction_fetch.c: move fetch and verify binpkgs and make use of xbps_fetch_file_digest

lib/Makefile

@@ -39,7 +39,7 @@ OBJS += package_msg.o transaction_shlibs.o
 OBJS += transaction_commit.o transaction_package_replace.o
 OBJS += transaction_prepare.o transaction_ops.o transaction_store.o
 OBJS += transaction_revdeps.o transaction_conflicts.o
-OBJS += transaction_files.o
+OBJS += transaction_files.o transaction_fetch.o
 OBJS += pubkey2fp.o package_fulldeptree.o
 OBJS += download.o initend.o pkgdb.o
 OBJS += plist.o plist_find.o plist_match.o archive.o