MEDIUM: applet: add basic support for an applet run queue

This will be needed so that we can schedule applets out of the streams.
For now nothing calls the queue yet.
diff --git a/Makefile b/Makefile
index 917f023..3c9ee24 100644
--- a/Makefile
+++ b/Makefile
@@ -703,7 +703,7 @@
        src/arg.o src/stick_table.o src/proto_uxst.o src/connection.o \
        src/proto_http.o src/raw_sock.o src/appsession.o src/backend.o \
        src/lb_chash.o src/lb_fwlc.o src/lb_fwrr.o src/lb_map.o src/lb_fas.o \
-       src/stream_interface.o src/dumpstats.o src/proto_tcp.o \
+       src/stream_interface.o src/dumpstats.o src/proto_tcp.o src/applet.o \
        src/session.o src/stream.o src/hdr_idx.o src/ev_select.o src/signal.o \
        src/acl.o src/sample.o src/memory.o src/freq_ctr.o src/auth.o \
        src/compression.o src/payload.o src/hash.o src/pattern.o src/map.o \