Add missing exports file

This exposes stasis_app_control_answer and allows
res_stasis_http_channels to load properly.


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@389217 65c4cc65-6c06-0410-ace0-fbb531ad65f3

res/res_stasis_answer.exports.in

+{
+	global:
+		LINKER_SYMBOL_PREFIXstasis_app_control_answer;
+	local:
+		*;
+};