GRIM: Fix misplaced override specifier in costumeemi.cpp
Merge pull request #803 from tombsar/master

GRIM: Syntax error when compiling with C++11 enabled
EMI: invalidate sortorder after detaching actors

- the order of the active actors is based on the effective sort order
  which is based on the sortorder of actors itself but also on the
  attached actors
- invalidate the sortorder also when detaching actors
- this fixes two glitches in the final end scene (guybrush is still
  displayed after falling from the cliff and monkey robot is drawn in
  the foreground)
Merge pull request #804 from chkr-private/sortorder-fixes

EMI: invalidate sortorder after changing attached actors
Merge pull request #794 from inguin/emi-walkto

GRIM/EMI: Ignore Actor:walkTo() if destination is unreachable
EMI: Reset sort order when changing sets

Some sets (e.g. the big monkey's engine room) set Guybrush's sort order
to a large value, causing him to become invisible in other places. This
patch resets the sort order for all actors when switching to a new set.