MINOR: httpclient: initialize the proxy

Initialize a proxy which contain a server for the raw HTTP, and another
one for the HTTPS. This proxy will use the global server log definition
and the 'option httplog' directive.

This proxy is internal and will only be used for the HTTP Client API.
diff --git a/Makefile b/Makefile
index e88ab30..84b1bc0 100644
--- a/Makefile
+++ b/Makefile
@@ -886,7 +886,8 @@
         src/hpack-tbl.o src/ebimtree.o src/auth.o src/ebsttree.o               \
         src/ebistree.o src/base64.o src/wdt.o src/pipe.o src/http_acl.o        \
         src/hpack-enc.o src/dict.o src/dgram.o src/init.o src/hpack-huff.o     \
-        src/freq_ctr.o src/ebtree.o src/hash.o src/version.o src/errors.o
+        src/freq_ctr.o src/ebtree.o src/hash.o src/version.o src/errors.o      \
+        src/http_client.o
 
 ifneq ($(TRACE),)
 OBJS += src/calltrace.o