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/terminal/terminalframebuffer.h

@@ -42,7 +42,7 @@
 #include <string>
 #include <list>
 
-#include "shared.h"
+#include "src/util/shared.h"
 
 /* Terminal framebuffer */