Some compiling warnings

When trying Valgrind I came across some compiling warnings with
USE_VALGRIND defined and --enable-cassert not configured. This is
mainly because in this case we have MEMORY_CONTEXT_CHECKING defined
while USE_ASSERT_CHECKING not defined.

aset.c: In function ‘AllocSetFree’:
aset.c:1027:10: warning: unused variable ‘chunk_size’ [-Wunused-variable]
Size chunk_size = block->endptr - (char *) pointer;
^
generation.c: In function ‘GenerationFree’:
generation.c:633:8: warning: variable ‘chunksize’ set but not used
[-Wunused-but-set-variable]
Size chunksize;
^

Attach a trivial patch for the fix.

Thanks
Richard