Add partial Dutch translation. Updates #1599.
Fix compilation with gcc
Use boost::thread in LibassSubtitlesProvider

libstdc++ 4.7's std::thread is missing sleep_for.
Fix compilation with gcc 4.7
Make automation depend on libaegisub
Add lua cflags for auto4_regex.cpp
Make pairs and ipairs call the appropriate metamethods when present

As is done in Lua 5.2. This makes it possible to use ipairs on the
subtitles object.
Actually define __ipairs on LuaAssFile
Set the maximum end time seen correctly in select-overlaps