Install a shared library

This required a fair bit of surgery because previously ostree.h
included otutil.h, but that's supposed to be a private library.

src/libostree/ostree-repo-libarchive.c

@@ -31,6 +31,8 @@
 #include "ostree-libarchive-input-stream.h"
 #endif
 
+#include "otutil.h"
+
 #ifdef HAVE_LIBARCHIVE
 
 static GFileInfo *