PlenaryCollection improvements
PlenaryCollection improvements

Add an extends() method to allow appending a list of plenaries. The
logger must be updated recursiverly when the appended plenary is a
collection itself.

Reviewed-By: Wesley Hertlein <ca32100e9f664971b15d1470ddc7f009d907efd3@morganstanley.com>

stdweird/aquilon,guillaume-philippon/aquilon,quattor/aquilon,stdweird/aquilon,stdweird/aquilon,quattor/aquilon,guillaume-philippon/aquilon,guillaume-philippon/aquilon,quattor/aquilon