Wim Taymans authored Jan 11, 2019 and Nicolas Dufresne committed Jan 11, 2019

We make an allocator for temporary lines and then use this for all
the steps in the conversion that can do in-place processing.

Keep track of the number of lines each step needs and use this to
allocate the right number of lines.

Previously we would not always allocate enough lines and we would
end up with conversion errors as lines would be reused prematurely.

Fixes #350