This function quickly checks to see if an identifier exists.
It does a quick head request to skip the overhead of item metadta retrieval.
This will also return FALSE if the identifier exists but is associated
with an item that is unavailable due to permission restrictions.
Usage
identifier_exists(sb_id, ...)
Value
Logical, TRUE or FALSE
Arguments
sb_id
An sbitem object or a character ScienceBase ID corresponding to the item
...
Additional parameters are passed on to GET, POST,
HEAD, PUT.