[fontloader] sync with Context as of 2014-12-07

Lots of changes, it’s been a while =)
[letterspace] add extra checks for character table

fix https://github.com/lualatex/luaotfload/issues/258

This fix was proposed by /u/saidai-no on Github.
[main] increase log threshold for font loader post-initialization message

The message violated our policy of not suppressing all non-error
messages on the terminal at log level 0. The faulty message was moved to
level 1 for both streams.

addresses https://github.com/lualatex/luaotfload/issues/256