Fix for loading of AVIs in BP. As discussed with The_E on IRC, this bug may have had a range of unintended consequences, although not clear why it hasn't been picked up already.

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9654 387891d4-d844-0410-90c0-e4c51a9137d3
Extra logging functionality for BMPMAN. This helped localise the fix in r9654.

git-svn-id: svn://svn.icculus.org/fs2open/trunk/fs2_open@9655 387891d4-d844-0410-90c0-e4c51a9137d3