[MINOR] add a weight divisor to the struct proxy

Under some circumstances, it will be useful to be able to have
a server's effective weight bigger than the user weight, and this
is particularly true for dynamic weight-based algorithms. In order
to support this, we add a "wdiv" member to the lbprm structure
which will always be used to divide the weights before reporting
them.
diff --git a/include/proto/backend.h b/include/proto/backend.h
index 7414ede..8fa8c83 100644
--- a/include/proto/backend.h
+++ b/include/proto/backend.h
@@ -42,6 +42,7 @@
 void recount_servers(struct proxy *px);
 void recalc_server_map(struct proxy *px);
 int be_downtime(struct proxy *px);
+void init_server_map(struct proxy *p);
 
 /*
  * This function tries to find a running server with free connection slots for