docs for "--execdir" confusing

[Eric Hanchrow]

In Version: 4.4.2-4ubuntu1, the info doc for --execdir says ``The
command is executed in the directory in which `find' was run.''
However, the doc for --exec says essentially the same thing: ``The
main difference is that the command is executed in the directory from
which `find' was invoked ...''

This is confusing -- I think the doc for --execdir should instead say
``The command is executed in the directory in which the file was
found''.

Also, the docs for --execdir claim that it's somehow more secure, but
it's not at all clear _why_.