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

bin/xbps-fetch/main.c

@@ -0,0 +1,14 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <xbps_api.h>
+
+int
+main(int argc, char **argv)
+{
+	if (argc != 2) {
+		printf("Usage: xbps-fetch [options] URL\n");
+		exit(EXIT_FAILURE);
+	}
+
+	return xbps_fetch_file(argv[1], ".");
+}