Allow Passing Flags to openFile function

Motivation

Currently, you can't pass flags (e.g. O_CREAT, O_EXCL, O_WRONLY) to openFile and withFile functions. In some applications, it is necessary to control underlying flags to Operating System's open function. Consider this Python code;

import os
import errno

flags = os.O_CREAT | os.O_EXCL | os.O_WRONLY
try:
	file_handle = os.open(target, flags)
except OSError as e:
	if e.errno == errno.EEXIST:  # Failed as the file already exists.
		pass
	else:  # Something unexpected went wrong so reraise the exception.
		raise
else:  # No exception, so the file must have been created successfully.
	
	with os.fdopen(file_handle, 'w') as file_obj:
            # here we are sure of 3 things
            # 1) File didn't exist before we try to open it
            # 2) We have exclusive access to it
            # 3) Checking for existence of file and creating it was an atomic operation, so no race-conditions there.

Proposal

Implement openFile' and withFile' functions, and OpenFileFlags data type, so that you can open files like in the following examples;

f <- openFile' "test.txt" (O_CREAT | O_EXCL | O_WRONLY)
withFile' "test.txt" (O_CREAT | O_EXCL | O_WRONLY) $ \h -> getlines h >>= mapM_ putStrLn