optimize read_file for smaller scalar slurps with no options

prepend_file()

	options: lock file?

edit_file()

	options: lock file?

edit_file_lines()

	options: lock file?

add options to read_dir
	prepend_dir
	grep filter qr or code ref


BUGS:

restart sysread/write after a signal (or check i/o count)

fix SEEK stuff

sent in patches:

check for objects/refs to filenames

add chmod mode to write_file

add perms (same as chmod?) to syswrite

check result of rename in atomic mode