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/run-command.c b/run-command.c
index 614d48f..e64bb08 100644
--- a/run-command.c
+++ b/run-command.c
@@ -8,6 +8,8 @@
 #include "thread-utils.h"
 #include "strbuf.h"
 #include "string-list.h"
+#include "trace.h"
+#include "trace2.h"
 #include "quote.h"
 #include "config.h"
 #include "packfile.h"