Checks all existing extradata keys and values to ensure that the set
that is being added doesn't already exist.

Closes #1802.

Removes the need for the RTL hacks in BaseGrid as the bugs have been
fixed properly in wx.

Closes #1818.

add '(Language)' after translated labels as suggested on the forums: http://forum.aegisub.org/viewtopic.php?f=5&t=66925#p91569

One spot was missed when converting stuff over to using error_Tag rather
than lua_error for stack unwinding on errors.

This is required for the gc metamethods to actually get run.

It hasn't actually been used for anything for a while, and if a single
normal-priority thread can make your system unresponsive it's time to
upgrade to an OS that's isn't garbage.

Dispatching to the main queue with GCD does not work when there is a
modal dialog active.

Closes #1795.

Targetting 10.7 makes the error handler segfault, and targetting 10.4
appears to work fine.

Closes #1791.

Trivially speeds up ProcFrame as constructing export filters isn't free
due to that it has to look up the translatable strings.

Building the lexer takes much longer than actually lexing, and since the
lexer is stateless there's no reason not to just make it static.

Fix compilation with PortAudio enabled

The old object returned by SelectObject has to be made active again
before the DC is destroyed or it doesn't get deleted.

Not only is it unnecessary, but it actively breaks the mapping of
user-friendly encoding names in the Export dialog to the real encoding
names.

Closes #1789.

It always fails when running under valgrind because valgrind does not
implement mmap functionality that LuaJIT requires.

Truncating the file at the first decoding error seems to cause a lot of
confusion, especially since the UI doesn't mention that it happened
anywhere.

Fixes the audio display timeline font changing based on what else is
being painted.