lib: add binary package internalization step

- internalize scripts so we can use them before unpacking packages.
- moves some required metadata checks out of the package unpack stage
  so errors do not leave the system in a half unpacked state.

xbps_transaction_files will be changed later to use the loaded
files.plist instead of opening each binary package on its own again.

lib/Makefile

@@ -43,6 +43,7 @@ OBJS += transaction_ops.o transaction_store.o transaction_check_replaces.o
 OBJS += transaction_check_revdeps.o transaction_check_conflicts.o
 OBJS += transaction_check_shlibs.o
 OBJS += transaction_files.o transaction_fetch.o transaction_pkg_deps.o
+OBJS += transaction_internalize.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