http: increase the replay count

Increase the permissible replay count; with multiple-step authentication
schemes (NTLM, Negotiate), proxy authentication and redirects, we need
to be mindful of the number of steps it takes to get connected.

7 seems high but can be exhausted quickly with just a single authentication
failure over a redirected multi-state authentication pipeline.

src/transports/http.c

@@ -108,7 +108,7 @@ typedef struct {
 	int parse_error;
 	int error;
 	unsigned parse_finished : 1,
-	    replay_count : 3;
+	    replay_count : 4;
 } http_subtransport;
 
 typedef struct {

src/transports/http.h

@@ -10,7 +10,7 @@
 
 #include "buffer.h"
 
-#define GIT_HTTP_REPLAY_MAX 7
+#define GIT_HTTP_REPLAY_MAX 15
 
 GIT_INLINE(int) git_http__user_agent(git_buf *buf)
 {