widgets.browsercolumn: fix hidden infostring with python2
core.tab: fix incorrect pointer on tab change

To reproduce the bug that this patch fixes, do:
1. start in a place where the second item is a directory that contains
   at least two files  (the usual $HOME with sort_directories_first=True
   will likely do)
2. open (and enter) a new tab with ^N
3. move down and right, entering the directory. The cursor is now on
   file 1
4. switch to tab 1, then back to tab 2
5. now the cursor is on file 2 instead of file 1.