CONCURRENT STREAM READ/WRITE

```
Description: NuttX only supports a single file pointer so reads and writes
must be from the same position. This prohibits implementation
of behavior like that required for fopen() with the "a+" mode.
According to the fopen man page:

"a+ Open for reading and appending (writing at end of file).
The file is created if it does not exist. The initial file
position for reading is at the beginning of the file, but
output is always appended to the end of the file."

At present, the single NuttX file pointer is positioned to the
end of the file for both reading and writing.
Status: Open
Priority: Medium. This kind of operation is probably not very common in
deeply embedded systems but is required by standards.
```