bootloader heap: Actually implement DEBUG_ALLOCATIONS.

The old define was really "check heap integrity", so it's split off.
In the userland test harness, this takes the total time spent in
the allocator from around 1ms to 14ms for all the allocations used
during a boot with "nightly" profile, so it seems acceptable to
enable it under KDEBUG.

Tested with both BIOS and EFI bootloaders, still works.

headers/private/kernel/util/SimpleAllocator.h

@@ -266,6 +266,9 @@ public:
 #ifdef DEBUG_MAX_HEAP_USAGE
 		fMaxHeapUsage = std::max(fMaxHeapUsage, fMaxHeapSize - fAvailable);
 #endif
+#ifdef DEBUG_ALLOCATIONS
+		memset(allocated, 0xcc, chunk->Size());
+#endif
 
 		return allocated;
 	}
@@ -306,7 +309,7 @@ public:
 
 		FreeChunk* freedChunk = FreeChunk::SetToAllocated(allocated);
 
-#ifdef DEBUG_ALLOCATIONS
+#ifdef DEBUG_VALIDATE_HEAP_ON_FREE
 		if (freedChunk->Size() > (fMaxHeapSize - fAvailable)) {
 			panic("freed chunk %p clobbered (%#zx)!\n", freedChunk,
 				freedChunk->Size());
@@ -321,6 +324,10 @@ public:
 			}
 		}
 #endif
+#ifdef DEBUG_ALLOCATIONS
+		for (uint32 i = 0; i < (freedChunk->Size() / 4); i++)
+			((uint32*)allocated)[i] = 0xdeadbeef;
+#endif
 
 		// try to join the new free chunk with an existing one
 		// it may be joined with up to two chunks