Added directive to specify content type of progress report

ngx_http_uploadprogress_module.c

     ngx_event_t                      cleanup;
     ngx_http_handler_pt              handler;
     u_char                           track;
+    ngx_str_t                        content_type;
 } ngx_http_uploadprogress_conf_t;
 
 typedef struct {
      0,
      NULL},
 
+    {ngx_string("upload_progress_content_type"),
+     NGX_HTTP_MAIN_CONF | NGX_HTTP_SRV_CONF | NGX_HTTP_LOC_CONF | NGX_CONF_TAKE1,
+     ngx_conf_set_str_slot,
+     NGX_HTTP_LOC_CONF_OFFSET,
+     offsetof(ngx_http_uploadprogress_conf_t, content_type),
+     NULL},
+
     ngx_null_command
 };
 
 	ngx_free(id);
 
     /* send the output */
-    r->headers_out.content_type.len = sizeof("text/javascript") - 1;
-    r->headers_out.content_type.data = (u_char *) "text/javascript";
+    r->headers_out.content_type = upcf->content_type;
 
     /* force no-cache */
     expires = r->headers_out.expires;
         *conf = *prev;
     }
 
+    ngx_conf_merge_str_value(conf->content_type, prev->content_type, "text/javascript");
+
     return NGX_CONF_OK;
 }