Display correct diff the context in split log view
In the log view, when scrolling across a commit, the diff view should
automatically switch to the commit whose context the cursor is on in
the log view. This commit changes things to catch the REQ_ENTER in the
log view and handle recalculation of the commit and diff display from
log_request, rather than delegating it to pager_request. In addition,
it also gets rid of unexpected upward scrolling of the log view.
Fixes GH #155
Signed-Off-By: Kumar Appaiah <a.kumar@alumni.iitm.ac.in>