`org-agenda-show-log' indicates if the the current agenda buffer has
log-mode enabled.  When building a new agenda buffer, it gets its
value from `org-agenda-start-with-log-mode'.  It is is semantically a
buffer local variable: when creating a new agenda buffer you expect it
to be set to the value in `org-agenda-start-with-log-mode'.  However,
2e9c2d71 while fixing an issue with sticky agendas rendered the
variable `org-agenda-log-mode' effectively global: toggling log mode
in a given agenda buffer modifies the global default for all agenda
buffers.  The same reasoning holds for clockreport mode.

This change ensures that a log or clockreport mode change made in one
agenda buffer does not propagate to other agenda buffers, existing or
new.  The change is however preserved on org-agenda-redo in the
initial agenda buffer, whether using sticky agendas or not.