Use a rb_ary_entry and not RARRAY_PTR()

For MRI, this doesn't make a difference, but on Rubinius this prevents
having to setup a backing store for copying over the internal array
pointers. This was the only case where RARRAY_PTR was used, other places
already use rb_ary_entry, so it should be a good change for consistency
as well.
Add Japanese Changelog for 1.5.7, 1.5.8 and 1.5.9
Fix translation of `reparent`
Using mini_portile to compile libxml2 and libxslt on any (non-windows) platform.
dependencies.yml is now the central location for library dependencies.

Note that this is for both windows cross-compile and packaged dependencies.
Upgrading libxml2 dependency from 2.7.7 to 2.7.8.

Affects only windows users at this time.
mini_portile is a gem dependency if we're building libxml2.
If we're building libxml2, include the tarballs in the gem manifest.
Upgrade mini_portile to support FTP, and removing my FTP-support hacks.
Compile libxml2 with the --with-threads option.
Setting fat-source dependency on libxml 2.8.0.
Making fat-source libraries the default, unless NOKOGIRI_USE_SYSTEM_LIBRARIES is set.
VERSION_INFO["libxml"]["source"] now indicates whether libxml2 comes from "system" or "packaged" libraries.
Version bump to 1.6.0.rc1 and CHANGELOG updates.
Fixing cross-compilation for Windows, and cleaning up extconf.rb
Deprecating Ruby 1.8.
mini_portile is now a runtime dependency
Package libxml2 and libxslt tarballs unless we're building windows or jruby gems.
VERSION_INFO now displays paths to libxml2 and libxslt if using the packaged libraries.
CHANGELOGs updated