patch 8.1.0614: placing signs can be complicated

Problem:    Placing signs can be complicated.
Solution:   Add functions for defining and placing signs.  Introduce a group
            name to avoid different plugins using the same signs. (Yegappan
            Lakshmanan, closes #3652)
diff --git a/src/proto/misc2.pro b/src/proto/misc2.pro
index 949ff72..b54337b 100644
--- a/src/proto/misc2.pro
+++ b/src/proto/misc2.pro
@@ -24,6 +24,7 @@
 char_u *alloc(unsigned size);
 char_u *alloc_id(unsigned size, alloc_id_T id);
 char_u *alloc_clear(unsigned size);
+char_u * alloc_clear_id(unsigned size, alloc_id_T id);
 char_u *alloc_check(unsigned size);
 char_u *lalloc_clear(long_u size, int message);
 char_u *lalloc(long_u size, int message);