py3: use integer division in histedit

Histedit uses the `/` operator, which does type conversion to float in
Python 3 instead of integer division likeon Python 2. Let's preserve
the Python 2 behavior by importing and using the `//` operator.

Differential Revision: https://phab.mercurial-scm.org/D8324

hgext/histedit.py

@@ -1267,7 +1267,7 b' def changeview(state, delta, unit):'
     num_lines = len(mode_state[b'patchcontents'])
     page_height = state[b'page_height']
     unit = page_height if unit == b'page' else 1
-    num_pages = 1 + (num_lines - 1) / page_height
+    num_pages = 1 + (num_lines - 1) // page_height
     max_offset = (num_pages - 1) * page_height
     newline = mode_state[b'line_offset'] + delta * unit
     mode_state[b'line_offset'] = max(0, min(max_offset, newline))