treewide: be explicit about dependence on trace.h & trace2.h

Dozens of files made use of trace and trace2 functions, without
explicitly including trace.h or trace2.h.  This made it more difficult
to find which files could remove a dependence on cache.h.  Make C files
explicitly include trace.h or trace2.h if they are using them.

Signed-off-by: Elijah Newren <newren@gmail.com>
Acked-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/unpack-trees.c b/unpack-trees.c
index 4a5522b..d41489b 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -17,6 +17,7 @@
 #include "sparse-index.h"
 #include "submodule.h"
 #include "submodule-config.h"
+#include "trace2.h"
 #include "fsmonitor.h"
 #include "object-store.h"
 #include "promisor-remote.h"