isOpen.character: Checks if there is an open connection to a file
Description
 Checks if there is an open connection to a file.
Usage
"isOpen"(pathname, rw=c("read", "write"), ...)
Arguments
rw
A character vector.
    If "read", a file is considered to be open if there exist an
    open connection that can read from that file.
    If "write", a file is considered to be open if there exist an
    open connection that can write to that file.
    Both these values may be specified.