Updated error message with up-to-date URLs
Treat target 'id' as name if ID not found for target delete

APPENG-3211

If targetId argument isn't found as a target ID, fall back to retreiving
all the targets and looking for a target name that matches.  If any are
found, then delete them.
Add trove version to 'list images' output

APPENG-3216

Use 'trailing_version', not the full trove version
add "(EBS)" to display type of EBS AMI imagedefs

APPENG-3208
Add a Y/N validation function to getYn

so that only Y or N responses are accepted, and other responses cause a
reprompt

for APPENG-3209