Add a few extra memory reserve calls to account for the extra space that
indentation needs.

These kinds of memory issues are hard to spot because the buffer is resized in
powers of 2 meaning that a miscalculation would only show any symptoms if the
required buffer size is estimated to be just below a 2 power but is actually
just above. Add a debug mode which replaces the 2 power scheme with reserving
only the memory explicitly requested and adds some overflow checks.

Unsetting it can lead to seg-faults. I don't think it's worth having to fix and
then test this undocumented permutation.