Switch to fully-qualified #include

Previously, mosh used extensive -I flags and all of the mosh-local
makes it really hard to tell what the proper dependency graph is, so
instead remove the -I arguments in favvor of $(top_srcdir) and qualify
the paths wherever they are used.

src/statesync/user.cc

@@ -33,9 +33,9 @@
 #include <assert.h>
 #include <typeinfo>
 
-#include "user.h"
-#include "fatal_assert.h"
-#include "userinput.pb.h"
+#include "src/statesync/user.h"
+#include "src/util/fatal_assert.h"
+#include "src/protobufs/userinput.pb.h"
 
 using namespace Parser;
 using namespace Network;