Added support for a cachedir to store downloaded binpkgs.

libxbps:
 * Added xbps_set_cachedir() and xbps_get_cachedir(). By default it's
   set to /var/cache/xbps if not specified and it's always relative
   to the root directory.
 * Move mkpath() code from sync_remote_pkgidc.c into its own file mkpath.c
   to use it in another parts of the code.
 * Added xbps_get_binpkg_local_path(), that returns the local path to
   a binary package file, stored in cachedir or local repo.
 * Remote pkg index files are now stored directly in metadir/repodir,
   skipping the arch directory because binpkgs are now in cachedir.

xbps-bin:
 * Added -c flag to set the cachedir.
 * Check sha256 hashes in the download stage so that it can check
   a downloaded binpkg immediately once is stored.
 * If a binpkg doesn't match the hash it will be refetched.

Bump XBPS_RELVER to 20091128.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20091128013841-kkcvk07lsqdr26w8

lib/Makefile

@@ -17,7 +17,7 @@ LIBFETCH_OBJS = fetch/common.o fetch/fetch.o fetch/file.o fetch/ftp.o fetch/http
 OBJS +=	configure.o cmpver.o depends.o download.o fexec.o findpkg.o
 OBJS +=	humanize_number.o orphans.o plist.o purge.o register.o remove.o
 OBJS +=	repository.o requiredby.o sha256.o sortdeps.o state.o
-OBJS +=	sync_remote_pkgidx.o unpack.o util.o pkgmatch.o
+OBJS +=	sync_remote_pkgidx.o unpack.o util.o pkgmatch.o mkpath.o
 OBJS +=	regpkgs_dictionary.o repository_plist.o repository_pool.o
 
 .PHONY: all