Eliminate duplication in surgery.

[deiferni]

Currently surgeries have pre-op checks done in perform. There is a certain level of duplication in those checks, when we touch them next we should attempt to reduce it. Namely

ftw.catalogdoctor/ftw/catalogdoctor/surgery.py

Lines 228 to 238 in f6d11cc

	rid = self.unhealthy_rid.rid
	if len(self.unhealthy_rid.paths) != 1:
	raise CantPerformSurgery(
	"Expected exactly one affected path, got: {}"
	.format(", ".join(self.unhealthy_rid.paths)))
	path = self.unhealthy_rid.paths[0]
	if self.catalog.uids[path] == rid:
	raise CantPerformSurgery(
	"Expected different rid in catalog uids mapping for path {}"
	.format(path))

and

ftw.catalogdoctor/ftw/catalogdoctor/surgery.py

Lines 256 to 272 in f6d11cc

	rid = self.unhealthy_rid.rid
	if len(self.unhealthy_rid.paths) != 1:
	raise CantPerformSurgery(
	"Expected exactly one affected path, got: {}"
	.format(", ".join(self.unhealthy_rid.paths)))
	path = list(self.unhealthy_rid.paths)[0]
	if path in self.catalog.uids:
	raise CantPerformSurgery(
	"Expected path to be absent from catalog uids {}"
	.format(path))
	portal = api.portal.get()
	obj = portal.unrestrictedTraverse(path, None)
	if obj is not None:
	raise CantPerformSurgery(
	"Unexpectedly found object at {}".format(path))