Replace bleeding-edge libevent with libevhtp.

A libevhtp package exists for recent releases of Linux distros. An
exception for these will come in a future patch.

Change-Id: I15b96be469b91f19c06c326fc52b42027c097df9
Bug: 26850406
Bug: 24204638
Reviewed-on: https://weave-review.googlesource.com/2384
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
diff --git a/third_party/third_party.mk b/third_party/third_party.mk
index 8a11e2d..7f651a2 100644
--- a/third_party/third_party.mk
+++ b/third_party/third_party.mk
@@ -64,15 +64,15 @@
 	rm -rf third_party/googletest
 
 ###
-# libevent (third_party, downloaded on build)
+# libevhtp (third_party, downloaded on build)
 
-third_party/include/event2/event.h :
-	@echo Downloading and building libevent...
-	DISABLE_LIBEVENT_TEST=1 third_party/get_libevent.sh
-	@echo Finished downloading and building libevent.
+third_party/lib/libevhtp.a : third_party/include/evhtp.h
+third_party/include/evhtp.h :
+	@echo Downloading and building libevhtp...
+	third_party/get_libevhtp.sh
+	@echo Finished downloading and building libevhtp.
 
-clean-libevent :
-	rm -rf third_party/include/ev* third_party/include/event2
-	rm -rf third_party/lib/libevent*
-	rm -rf third_party/libevent
-
+clean-libevhtp :
+	rm -rf third_party/include/evhtp.h third_party/include/evhtp-config.h third_party/include/evthr.h third_party/include/htparse.h
+	rm -rf third_party/lib/libevhtp.a
+	rm -rf third_party/libevhtp