std: reworking how some net and libuv modules are exported in the rc

.. turns out that, without the export, the modules aren't accessible
outside of the crate, itself. I thought that, by importing some module
into another (nesting it) and exporting from that nested module (which
is, itself, exported from std.rc) that my mod would be in the build
artifact. This doesn't appear to be the case. learning is fun!

src/libstd/std.rc

@@ -13,7 +13,8 @@
 use core(vers = "0.2");
 import core::*;
 
-export net, uv;
+export net, net_tcp;
+export uv, uv_ll, uv_hl, uv_global_loop;
 export c_vec, util, timer;
 export bitv, deque, fun_treemap, list, map, smallintmap, sort, treemap;
 export rope, arena;