BUG/MEDIUM: httpclient/cli: free of unallocated hc->req.uri

httpclient_new() sets the hc->req.uri ist without duplicating its
memory, which is a problem since the string in the ist could be
inaccessible at some point. The API was made to use a ist which was
allocated dynamically, but httpclient_new() didn't do that, which result
in a crash when calling istfree().

This patch fixes the problem by doing an istdup()

Fix issue #1452.
diff --git a/src/http_client.c b/src/http_client.c
index fe85f05..4e5ef7c 100644
--- a/src/http_client.c
+++ b/src/http_client.c
@@ -535,7 +535,7 @@
 		goto err;
 
 	hc->caller = caller;
-	hc->req.url = url;
+	hc->req.url = istdup(url);
 	hc->req.meth = meth;
 
 	return hc;