Bugfix: if dump() was called, del can't write keys during flush.
Bugfix: if dump() was called, del can't write keys during flush.

This just checks if dump has been called (by seeing if self.path
exists).  It dump was called, then delete the contents of self.inmem
but don't move them to disk or write keys.

quantopian/chest,pombredanne/chest,blaze/chest,maxhutch/chest,ContinuumIO/chest,llllllllll/chest,mrocklin/chest