http: make http_get_file() external

This method will be used in an upcoming extension of git-remote-curl to
download a single file over HTTP(S) by request.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/http.c b/http.c
index 229da4d..04e7314 100644
--- a/http.c
+++ b/http.c
@@ -1945,8 +1945,8 @@ int http_get_strbuf(const char *url,
  * If a previous interrupted download is detected (i.e. a previous temporary
  * file is still around) the download is resumed.
  */
-static int http_get_file(const char *url, const char *filename,
-			 struct http_get_options *options)
+int http_get_file(const char *url, const char *filename,
+		  struct http_get_options *options)
 {
 	int ret;
 	struct strbuf tmpfile = STRBUF_INIT;