Assorted fixes

This is a collection of fixes that should improve the likelihood of it being picked up by package maintainers; it also includes a few memory fixes.

Package / build changes:

* No longer bundle `libuv`; instead, link against an installation using `--with-uv[=DIR]`; it doesn't yet assert a particular version, it won't build on 0.12 so that needs fixing later on.
* Only build the http parser when `--enable-httpparser` is used and make sure it builds with and without. I've created two separate source files for ease of maintenance. Later on we could separate it into its own module (but still within the same extension).
* Remove Darwin framework inclusion; my `clang` didn't like those.
* Add dependency on `sockets` extensions in `config.m4`.
* Removed 5.3 target and added 5.6 target.

Bug fixes:

* Updated some test cases that were dependent on resource id's; it now uses `EXPECTF`.
* Fixed two memory overflows in `uv_cwd()` and `uv_exepath()`; it also uses the `MAXPATHLEN`.
* Fixed parser test case.