list: make our list macros a bit easier to use by not requring type spec on each invocation

We can determine the list entry type via the typeof() gcc construct, and
so we should to make the macros much shorter to use.

src/bootchart/bootchart.c

@@ -332,7 +332,7 @@ int main(int argc, char *argv[]) {
 
         log_uptime();
 
-        LIST_HEAD_INIT(struct list_sample_data, head);
+        LIST_HEAD_INIT(head);
 
         /* main program loop */
         for (samples = 0; !exiting && samples < arg_samples_len; samples++) {
@@ -406,7 +406,7 @@ int main(int argc, char *argv[]) {
                         /* calculate how many samples we lost and scrap them */
                         arg_samples_len -= (int)(newint_ns / interval);
                 }
-                LIST_PREPEND(struct list_sample_data, link, head, sampledata);
+                LIST_PREPEND(link, head, sampledata);
         }
 
         /* do some cleanup, close fd's */

src/bootchart/svg.c

@@ -81,7 +81,7 @@ static void svg_header(void) {
         struct list_sample_data *sampledata_last;
 
         sampledata = head;
-        LIST_FIND_TAIL(struct list_sample_data, link, sampledata, head);
+        LIST_FIND_TAIL(link, sampledata, head);
         sampledata_last = head;
         LIST_FOREACH_BEFORE(link, sampledata, head) {
                 sampledata_last = sampledata;