Fix two more header inclusion mistakes.

src/hydro.h

@@ -23,8 +23,10 @@
 #include "../config.h"
 
 /* Local headers. */
+#include "const.h"
 #include "hydro_properties.h"
 #include "kernel_hydro.h"
+#include "part.h"
 
 /* Import the right functions */
 #if defined(MINIMAL_SPH)

src/hydro_properties.c

@@ -26,6 +26,7 @@
 
 /* Local headers. */
 #include "adiabatic_index.h"
+#include "equation_of_state.h"
 #include "common_io.h"
 #include "dimension.h"
 #include "error.h"