cache: move ensure_full_index() to cache.h

Soon we will insert ensure_full_index() calls across the codebase.
Instead of also adding include statements for sparse-index.h, let's just
use the fact that anything that cares about the index already has
cache.h in its includes.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Reviewed-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -350,6 +350,7 @@ void add_name_hash(struct index_state *istate, struct cache_entry *ce);
 void remove_name_hash(struct index_state *istate, struct cache_entry *ce);
 void free_name_hash(struct index_state *istate);
 
+void ensure_full_index(struct index_state *istate);
 
 /* Cache entry creation and cleanup */
 

sparse-index.h

@@ -2,7 +2,6 @@
 #define SPARSE_INDEX_H__
 
 struct index_state;
-void ensure_full_index(struct index_state *istate);
 int convert_to_sparse(struct index_state *istate);
 
 struct repository;