* UpdateIssueUsersByMentions was calling database write operations while a transaction session was in progress. MailParticipants was failing silently because of the SQLITE_LOCKED error. Make sure failures in MailParticipants enter the log, and pass on the transaction context. issue: let caller pass in database context, and use it issue_comment: obtain database context to pass to UpdateIssueMentions issue_comment: log any error from call to MailParticipants issue_mail: pass on database context to UpdateIssueMentions * issue: forgot debug statement