Merge branch 'tc/curl-with-backports'

Updates to the HTTP layer we made recently unconditionally used
features of libCurl without checking the existence of them, causing
compilation errors, which has been fixed.  Also migrate the code to
check feature macros, not version numbers, to cope better with
libCurl that vendor ships with backported features.

* tc/curl-with-backports:
  http: use a feature check to enable GSSAPI delegation control
  http: fix handling of missing CURLPROTO_*

http.c

@@ -91,7 +91,7 @@ static struct {
 	 * here, too
 	 */
 };
-#if LIBCURL_VERSION_NUM >= 0x071600
+#ifdef CURLGSSAPI_DELEGATION_FLAG
 static const char *curl_deleg;
 static struct {
 	const char *name;
@@ -352,7 +352,7 @@ static int http_options(const char *var, const char *value, void *cb)
 	}
 
 	if (!strcmp("http.delegation", var)) {
-#if LIBCURL_VERSION_NUM >= 0x071600
+#ifdef CURLGSSAPI_DELEGATION_FLAG
 		return git_config_string(&curl_deleg, var, value);
 #else
 		warning(_("Delegation control is not supported with cURL < 7.22.0"));
@@ -677,6 +677,7 @@ void setup_curl_trace(CURL *handle)
 	curl_easy_setopt(handle, CURLOPT_DEBUGDATA, NULL);
 }
 
+#ifdef CURLPROTO_HTTP
 static long get_curl_allowed_protocols(int from_user)
 {
 	long allowed_protocols = 0;
@@ -692,6 +693,7 @@ static long get_curl_allowed_protocols(int from_user)
 
 	return allowed_protocols;
 }
+#endif
 
 static CURL *get_curl_handle(void)
 {
@@ -717,7 +719,7 @@ static CURL *get_curl_handle(void)
 	curl_easy_setopt(result, CURLOPT_HTTPAUTH, CURLAUTH_ANY);
 #endif
 
-#if LIBCURL_VERSION_NUM >= 0x071600
+#ifdef CURLGSSAPI_DELEGATION_FLAG
 	if (curl_deleg) {
 		int i;
 		for (i = 0; i < ARRAY_SIZE(curl_deleg_levels); i++) {
@@ -790,7 +792,7 @@ static CURL *get_curl_handle(void)
 #elif LIBCURL_VERSION_NUM >= 0x071101
 	curl_easy_setopt(result, CURLOPT_POST301, 1);
 #endif
-#if LIBCURL_VERSION_NUM >= 0x071304
+#ifdef CURLPROTO_HTTP
 	curl_easy_setopt(result, CURLOPT_REDIR_PROTOCOLS,
 			 get_curl_allowed_protocols(0));
 	curl_easy_setopt(result, CURLOPT_PROTOCOLS,