The BZR xml output plugin can use some encodings that are not recognized
by expat, which leads to "Error parsing bzr log xml: unknown encoding".
This works around the problem by giving expat a mapping, and adds a
test. Patch from Tom Vercauteren. See issue #6857.
This creates cmCTestBZR to drive CTest Update handling on bzr-based work
trees. Currently we always update to the head of the remote tracking
branch (bzr pull), so the nightly start time is ignored for Nightly
builds. A later change will address this. Patch from Tom Vercauteren.
See issue #6857.