NOT TESTED; NOT READY FOR PRIME TIME.
Archived here for backup/review purposes.

Initial version; unifies tbswapout and tbswapin into one
script.

Should be just like tbswapin/out except:
tbswapin  foo bar => tbswap in  foo bar
tbswapout foo bar => tbswap out foo bar

The main win here is that doSwapin() is a function, as is doSwapout().
If doSwapin() fails, actual doSwapout() code can be called.

Also includes retry framework
(functionalizing doSwapin and doSwapout makes retrying much cleaner.)