Cleanup: move tag functions into own translation unit

Make dive.h a bit slimmer. It's only a drop in the bucket - but at
least when modifying tag functions not the *whole* application is
rebuilt anymore.

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

core/load-git.c

@@ -22,6 +22,7 @@
 #include "membuffer.h"
 #include "git-access.h"
 #include "qthelper.h"
+#include "tag.h"
 
 const char *saved_git_id = NULL;