This patch adds $ferror() support. This is enhanced over what the standard
says needs to be supported. All file I/O routines set/clear the errno flag,
This allows $ferror() to check when an invalid fd/MCD is passed to a
system task. The $ferror() fd is only checked if errno is not set since
all the other routines will set EBADF when they are called. This allows us
to test the output from $fopen() which sets the fd to zero (an invalid fd)
when it has a problem.
The following bugs (changes) are also fixed:
Fix $fdisplay*, $fwrite*, $fstrobe*, $fflush, $fclose to not accept 0 as
a valid MCD.
For the $fdisplay*, $fwrite* and $fstrobe tasks an invalid fd/MCD is now
a warning instead of an error like the other file I/O routines.
Modify $fputc() to be a function and return a value like $ungetc().
Modify $ungetc() to return a value like the standard dictates (-1 on
error else 0) and pass the value as a full int to get EOF as an error.
Remove some extra checks that could not happen in $fseek() and to
be safe convert the numeric codes to the system symbolic values.
Skip $fstrobe callback when the fd/MCD is closed. The standard says
we need to cancel the callback, but we currently do not have the
ability to do that so just skipping this will work for now.
Free the argument handle when $fscanf() is called with an invalid fd
(memory leak).
ce89a68735