Implemented support for working with remote repositories.

libfetch from NetBSD's pkgsrc has been imported into lib/fetch, but
the objects are embedded into libxbps. Only a public function to fetch
files has been implemented: xbps_fetch_file().

The library now is built with -fvisibility=hidden by default, and
exported symbols are the ones that use the SYMEXPORT macro.

The code works well enough, but will need many more cleanups.

--HG--
extra : convert_revision : xtraeme%40gmail.com-20091027004600-0lq9aao67lisbzxv

lib/fetch/errlist.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+# $NetBSD: errlist.sh,v 1.2 2008/10/06 12:58:29 joerg Exp $
+
+printf "static struct fetcherr $1[] = {\n"
+while read code type msg; do
+	[ "${code}" = "#" ] && continue
+	printf "\t{ ${code}, FETCH_${type}, \"${msg}\" },\n"
+done < $3
+
+printf "\t{ -1, FETCH_UNKNOWN, \"Unknown $2 error\" }\n"
+printf "};\n"