shar: support directory args from find

[mknos]

• DragonFly, FreeBSD, NetBSD and OpenBSD manual pages share the example of using the find command to provide the arguments to shar
• The output of find lists a directory before the files it contains
• Add support for this usage by writing mkdir command on output if an argument is a directory
• mkdir still runs for the "." directory in the following example but this is consistent with the OpenBSD version
• Print directory name with "/" suffix when extracting
• Update POD

perl ~/ppt/shar $(find . -print) > ~/new.shar

cd; sh new.shar
x - ./
x - ./b/
x - ./b/false
x - ./apply