issue-464: correctly handle realloc after memalign in debugalloc

debug memalign is creating special header block to allow us to find
real allocated block. And previous implementation of data copying
wasn't taking that into account and was copying that "alignment
header" into newly allocated block.
eliminated useless BASE_XXX defines in debugallocation.cc

And closed TODO entry for that.
removed unused "using" in malloc_extension_test.cc
avoid crash in DebugMallocImplementation::GetOwnership

It was possible that if GetOwnership is passed pointer to memory not
owned by tcmalloc, it would crash. Or incorrectly return
owned. I.e. due to indirection in FromRawPointer.

New implementation prevents that, but introduces different bug
instead. New implementation incorrectly returns "not owned" for
memalign chunks with big alignment. But in can be argued that passing
pointer returned from different memalign implementation did not work
previously too.
added debugallocation check for offset_ corruption

It was previously possible (although unlikely) for damaged offset_ field
to lead FromRawPointer implementation into different MallocBlock.

As is usual with any damage, it's best to catch errors at earliest
possible time.