record attachments' dropping/truncation as txns
test attachment dropping/truncation
make attachment truncate/drop and error txns more noticeable

color scheme is from cloos++
refactor email sent failure system error txn to use the same tech as Attachment Truncate/Drop.

it's more simple and secure: by specifying ActivateScrips to 0, it won't cause infinite-loop,
which could happen if the system error txn triggers some scrips to send mails.
Merge branch '4.2/record-attachments-dropping' into 4.2-trunk