http: fix handling of missing CURLPROTO_*

Commit aeae4db1 refactored the handling of the curl protocol
restriction support into a function but failed to add a version
check for older versions of curl that lack CURLPROTO_* support.

Add the missing check and at the same time convert it to a feature
check instead of a version based check.  This is done to ensure that
vendor supported curl versions that have had CURLPROTO_* support
backported are handled correctly.

Signed-off-by: Tom G. Christensen <tgc@jupiterrise.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

http.c

@@ -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)
 {
@@ -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,