s3exists: Determine whether object exists on S3.
In robertzk/s3mpi: R message passing interface using S3 storage

Test whether or not the given object exists at the give S3 path.

1	s3exists(name, path = s3path())

`name`	string. Name of file to look for
`path`	string. Path to file. If missing, the entire s3 path must be provided in name.

## Not run: 
s3exists("my/key") # Will look in bucket given by getOption("s3mpi.path") or
from a system environment variable.
  # For example, if this option is "s3://mybucket/", then this query
  # will check for existence of the \code{s3://mybucket/my/key} S3 path.

s3exists("my/key", "s3://anotherbucket/") # We can of course change the bucket.

## End(Not run)