Add locking to filehandle creation

[dagolden]

Many modules take a filehandle for input or output (e.g. IO::Compress::Gzip) and they don't bother locking. We should make it easy to produce locked handles from filehandle.

$path->filehandle({ mode => ">", binmode => ":utf8", lock_ex => 1})

or

$path->filehandle( $mode, $binmode, $locked );

Or something along those lines. In the latter case we can guess LOCK_EX or LOCK_SH based on the $mode.

[dagolden]

shipped it already