little coding style fixes, fix compilation warning

include/util.h

@@ -104,7 +104,7 @@ void check_error(xcb_connection_t *conn, xcb_void_cookie_t cookie,
  */
 char *convert_utf8_to_ucs2(char *input, int *real_strlen);
 
-/*
+/**
  * This function resolves ~ in pathnames.
  * It may resolve wildcards in the first part of the path, but if no match
  * or multiple matches are found, it just returns a copy of path as given.
@@ -112,13 +112,20 @@ char *convert_utf8_to_ucs2(char *input, int *real_strlen);
  */
 char *resolve_tilde(const char *path);
 
-/*
+/**
  * Checks if the given path exists by calling stat().
  *
  */
 bool path_exists(const char *path);
 
-/*
+
+/**
+ * Returns the name of a temporary file with the specified prefix.
+ *
+ */
+char *get_process_filename(const char *prefix);
+
+/**
  * Restart i3 in-place
  * appends -a to argument list to disable autostart
  *