Large alloc fix (#178)

* Improved malloc style tests

Added comprehensive testing of realloc, and other minor improvements
to reporting errors.

* Fix realloc resizing for large sizeclasses.

The rounding by sizeclass was incorrect for large allocation.  This fixes
that.

* Ensure alloc_size is committed

There is an awkward interaction between alloc_size and
committing only what is requested.  If the user assumes
everything up to alloc_size is available, then we need to
either store the more precise size for alloc_size to return
or commit the whole 2^n range, so that alloc_size stays simple.

This changes to just make the whole range committed.
In the future, we might want to store a more precise size, so
that the allocation can be sized more precisely.

* Reduce size of objects.

src/mem/largealloc.h

@@ -366,8 +366,7 @@ namespace snmalloc
         p = memory_provider.template reserve<false>(large_class);
         if (p == nullptr)
           return nullptr;
-        memory_provider.template notify_using<zero_mem>(
-          p, bits::align_up(size, OS_PAGE_SIZE));
+        memory_provider.template notify_using<zero_mem>(p, rsize);
       }
       else
       {
@@ -390,8 +389,7 @@ namespace snmalloc
           // Passing zero_mem ensures the PAL provides zeroed pages if
           // required.
           memory_provider.template notify_using<zero_mem>(
-            pointer_offset(p, OS_PAGE_SIZE),
-            bits::align_up(size, OS_PAGE_SIZE) - OS_PAGE_SIZE);
+            pointer_offset(p, OS_PAGE_SIZE), rsize - OS_PAGE_SIZE);
         }
         else
         {
@@ -399,6 +397,8 @@ namespace snmalloc
           if constexpr (zero_mem == YesZero)
             memory_provider.template zero<true>(
               p, bits::align_up(size, OS_PAGE_SIZE));
+          else
+            UNUSED(size);
         }
       }