GitLab

Add the new function less_than_a_screenful() to accomplish this.
It uses go_back_chunks() to count the number of softwrapped chunks
between the end point and the starting point of the paste.

Now softwrap mode and non-softwrap mode behave the same way when
uncutting fewer than editwinrows rows of text.  Accordingly, remove
the call to ensure_line_is_visible(), as it no longer applies.