patch 8.1.1414: alloc() returning "char_u *" causes a lot of type casts

Problem:    Alloc() returning "char_u *" causes a lot of type casts.
Solution:   Have it return "void *". (Mike Williams)  Define ALLOC_ONE() to
            check the simple allocations.
diff --git a/src/blob.c b/src/blob.c
index ec305d6..cbd26b9 100644
--- a/src/blob.c
+++ b/src/blob.c
@@ -22,7 +22,7 @@
     blob_T *
 blob_alloc(void)
 {
-    blob_T *blob = (blob_T *)alloc_clear(sizeof(blob_T));
+    blob_T *blob = ALLOC_CLEAR_ONE(blob_T);
 
     if (blob != NULL)
 	ga_init2(&blob->bv_ga, 1, 100);