girepository: Properly acquire and check pointer values

On Windows (Visual Studio at least), unsigned longs are always 4 bytes,
on both 32-bit and x64 Windows, so we cannot use unsigned longs to deal
with pointers on 64-bit builds, as pointers are 8 bytes on 64-bit
Windows, which may well render the pointer (which we acquired from
libffi) invalid.

This will fix crashes in PyGObject which are manifested when launching
the cairo-demo example sript (intermittent) and when clicking on
"Interactive Dialog" button in the Dialog demo in the PyGObject GTK+
Code demos before entering anything in Entry 1 and Entry 2, when running
on x64 Visual Studio builds of the GTK+/PyGObject stack.

Also use size_t instead of unsigned long in gthash.c when we check that
memory & 0x3 is 0, to silence compiler warnings from enabling /Wp64,
which is used to detect portability problems on Visual Studio when
doing x86->x64 code builds.

https://bugzilla.gnome.org/show_bug.cgi?id=702788

gicallableinfo.c

@@ -535,7 +535,7 @@ gi_type_info_extract_ffi_return_value (GITypeInfo                  *return_info,
                 arg->v_int32 = (gint32) ffi_value->v_long;
                 break;
             default:
-                arg->v_pointer = (gpointer) ffi_value->v_ulong;
+                arg->v_pointer = (gpointer) ffi_value->v_pointer;
                 break;
             }
 
@@ -543,7 +543,7 @@ gi_type_info_extract_ffi_return_value (GITypeInfo                  *return_info,
         }
         break;
     default:
-        arg->v_pointer = (gpointer) ffi_value->v_ulong;
+        arg->v_pointer = (gpointer) ffi_value->v_pointer;
         break;
     }
 }

gthash.c

@@ -158,7 +158,7 @@ _gi_typelib_hash_builder_pack (GITypelibHashBuilder *builder, guint8* mem, guint
   g_return_if_fail (builder->buildable);
 
   g_assert (len >= builder->packed_size);
-  g_assert ((((unsigned long)mem) & 0x3) == 0);
+  g_assert ((((size_t)mem) & 0x3) == 0);
 
   memset (mem, 0, len);
 
@@ -202,7 +202,7 @@ _gi_typelib_hash_search (guint8* memory, const char *str, guint n_entries)
   guint32 dirmap_offset;
   guint32 offset;
 
-  g_assert ((((unsigned long)memory) & 0x3) == 0);
+  g_assert ((((size_t)memory) & 0x3) == 0);
   mph = ((guint32*)memory)+1;
 
   offset = cmph_search_packed (mph, str, strlen (str));