Update libuv to v0.11.19

I extracted this from #460. The version of libuv that is currently vendored lacks a couple of Android-related fixes. The libuv and gyp commits are large, but the other three show the changes to cjdns. All the source code changes are in the last commit:

- uv_err_t and uv_last_error() have been removed
- uv_buf_t allocation has changed
- Removed logging that relied only on uv_last_error()
- Removed logging of dead conditions
- IPv4 and IPv6 have been merged
- tree.h has been made public

Please review this carefully, the tests are passing - but this is the first time I seriously work with C, and it's likely that a few happy accidents happen.

Will test tomorrow on my Pis.