environment.h: move declarations for environment.c functions from cache.h

Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/range-diff.c b/range-diff.c
index 1bfc612..815fb24 100644
--- a/range-diff.c
+++ b/range-diff.c
@@ -1,4 +1,5 @@
 #include "cache.h"
+#include "environment.h"
 #include "gettext.h"
 #include "range-diff.h"
 #include "string-list.h"