add prechangegroup and pretxnchangegroup hooks.
prechangegroup lets you stop push, pull or unbundle before it begins.
pretxnchangegroup lets you inspect changegroup before transaction is
committed, and roll back if you not like it.
changeset: 0:acb14030fe0a
tag: tip
user: test
date: Thu Jan 1 00:00:00 1970 +0000
summary: test
changeset: 1:863197ef0378
tag: tip
user: test
date: Thu Jan 1 00:00:00 1970 +0000
summary: Added tag bleah for changeset acb14030fe0a21b60322c440ad2d20cf7685a376
changeset: 0:acb14030fe0a
tag: bleah
user: test
date: Thu Jan 1 00:00:00 1970 +0000
summary: test
abort: working copy of .hgtags is changed (please commit .hgtags manually)
failed
use of 'hg tag NAME [REV]' is deprecated, please use 'hg tag [-r REV] NAME' instead
abort: use only one form to specify the revision
failed
use of 'hg tag NAME [REV]' is deprecated, please use 'hg tag [-r REV] NAME' instead
acb14030fe0a21b60322c440ad2d20cf7685a376 bleah
acb14030fe0a21b60322c440ad2d20cf7685a376 bleah0
863197ef03781c4fc00276d83eb66c4cb9cd91df bleah1
abort: '\n' cannot be used in a tag name
abort: ':' cannot be used in a tag name