emacs: more flexible and consistent tagging operations

[Dmitry Kurochkin]

Changes:

v3:

* merged 3 `notmuch-show-tag-all'-related patches into one

* add patch to clean up tagging function argument names

* fix other comments from Austin's reviews [5,6]

v2:

* add patch to remove "No tags given" error from `notmuch-tag' as
  suggested by Austin in [1]

* split patch 3 in two (search and show) for easier review

* add patch with NEWS entry

* rename `notmuch-{search,show}-operate-all' to
  `notmuch-{search,show}-tag-all'

* fix other comments from Austin's reviews [2,3,4]

Regards,
  Dmitry

[1] id:"20120129231650.GK17991 at mit.edu"
[2] id:"20120129225710.GG17991 at mit.edu"
[3] id:"20120129230229.GI17991 at mit.edu"
[4] id:"20120129231120.GJ17991 at mit.edu"
[5] id:"20120130044806.GM17991 at mit.edu"
[6] id:"20120130050402.GP17991 at mit.edu"