drop_exists: Checks to see if a file/folder exists on Dropbox
Description
Since many file operations such as move, copy, delete and history can only act
on files that currently exist on a Dropbox store, checking to see if the
path is valid before operating prevents bad API calls from being sent
to the server. This functions returns a logical response after checking if a
file path is valid on Dropbox.
The Dropbox token generated by drop_auth.
rdrop2 will try to automatically locate your local credential cache and use
them. However, if the credentials are not found, the function will initiate
a new authentication request. You can override this by pointing to a
different location where your credentials are stored.