Changes to kernel_args to make it identical for x86 and x86_64.

* Added a FixedWidthPointer template class which uses 64-bit storage to hold
  a pointer. This is used in place of raw pointers in kernel_args.
* Added __attribute__((packed)) to kernel_args and all structures contained
  within it. This is necessary due to different alignment behaviour for
  32-bit and 64-bit compilation with GCC.
* With these changes, kernel_args will now come out the same size for both
  the x86_64 kernel and the loader, excluding the preloaded_image structure
  which has not yet been changed.
* Tested both an x86 GCC2 and GCC4 build, no problems caused by these changes.

headers/private/kernel/boot/addr_range.h

@@ -13,13 +13,13 @@
 typedef struct addr_range {
 	uint64 start;
 	uint64 size;
-} addr_range;
+} _PACKED addr_range;
 
 
 typedef struct phys_addr_range {
 	phys_addr_t	start;
 	phys_size_t	size;
-} phys_addr_range;
+} _PACKED phys_addr_range;
 
 
 #ifdef __cplusplus