Clarify that http-push being temporarily disabled with older cURL

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/RelNotes-1.5.4.txt

@@ -10,8 +10,18 @@ Removal
  * As git-commit and git-status have been rewritten, "git runstatus"
    helper script lost all its users and has been removed.
 
- * Curl library older than 7.10 is not supported by "git http-push",
-   as it does not work without CURLM.
+
+Temporarily Disabled
+--------------------
+
+ * "git http-push" is known not to work well with cURL library older
+   than 7.16, and we had reports of repository corruption.  It is
+   disabled on such platforms for now.  Unfortunately, 1.5.3.8 shares
+   the same issue.  In other words, this does not mean you will be
+   fine if you stick to an older git release.  For now, please do not
+   use http-push from older git with cURL older than 7.16 if you
+   value your data. A proper fix will hopefully materialize in
+   later versions.
 
 
 Deprecation notices

Documentation/git-http-push.txt

@@ -15,6 +15,9 @@ DESCRIPTION
 Sends missing objects to remote repository, and updates the
 remote branch.
 
+*NOTE*: This command is temporarily disabled if your cURL
+library is older than 7.16, as the combination has been reported
+not to work and sometimes corrupts repository.
 
 OPTIONS
 -------

http.h

@@ -8,6 +8,14 @@
 
 #include "strbuf.h"
 
+/*
+ * We detect based on the cURL version if multi-transfer is
+ * usable in this implementation and define this symbol accordingly.
+ * This is not something Makefile should set nor users should pass
+ * via CFLAGS.
+ */
+#undef USE_CURL_MULTI
+
 #if LIBCURL_VERSION_NUM >= 0x071000
 #define USE_CURL_MULTI
 #define DEFAULT_MAX_REQUESTS 5