public freebusy crashing - wip

This pull request contains part of patches done for public freebusy.
Although not yet fully implemented, I would like those patches to get in as there are
few that are very important imho like 54325f3, 3e0eb4d, 281bff9, f13c23d
why not depend on libmapi.$(SHLIBEXT).$(PACKAGE_VERSION) rather than just having it in the build line ?