Backport commit 123ddec from Emacs master branch

Backport commit 123ddec from Emacs master branch

* doc/org.texi (Dynamic blocks):
* lisp/org-archive.el (org-archive-subtree)
(org-archive-to-archive-sibling):
* lisp/org-clock.el (org-resolve-clocks, org-clock-get-sum-start)
(org-clock-special-range):
* lisp/org-timer.el (org-timer-seconds):
* lisp/org.el (org-read-date-analyze, org-get-cursor-date):
* lisp/ox-html.el (org-html-format-spec):
* lisp/ox-icalendar.el (org-icalendar--vtodo):
Omit unnecessary call to current-time.
* lisp/org.el (org-get-cursor-date):
Don't call current-time twice to get the current time stamp,
as this can lead to inconsistent results.
* lisp/org-compat.el (org-float-time):
Simplify to an alias because time-to-seconds now behaves like float-time
with respect to nil arg.
* lisp/org-clock.el (org-clock-get-table-data): Omit unnecessary, lossy
conversion from floating point to Emacs time and back.
(org-resolve-clocks): Prefer two-argument floor.

Simplify use of current-time and friends.
123ddec7f807f4bd7400bbbe08219afb02269c00
Paul Eggert
Tue Oct 28 18:42:51 2014 -0700