Create flags to be verbose and to recursively create snapshots

• Use getops for option handling.
• Create snapshots again when a scrub is in progress.
• Let the -r flag be specified for individual datasets
  • To handle parsing the '-r' flags, the create function was broken off into two
    functions: create_parse() and create(). create() creates one snapshot per call.
• Use upper case for global variables.
• Created helper functions pool_ok and pool_scrub.
• Minor changes to warning messages.
• POSIX sh does not support local, so initialize variables intended to be local
  to a function.