[O] sexp timestamp causing agenda compilation issues as of 8517be79b5c1

[Kyle Machulis]

As of commit 8517be79b5c1fe165d23ea65ad70a282e9c595bb (bisected to
find this), agenda compilation died with the following backtrace for
me:

Debugger entered--Lisp error: (error "Bad timestamp `'
Error was: (Not a standard Org-mode time string: )")
  signal(error ("Bad timestamp `'\nError was: (Not a standard Org-mode
time string: )"))
  error("Bad timestamp `%s'%s\nError was: %s" "" "" ("Not a standard
Org-mode time string: "))
  byte-code(...)
  org-time-string-to-absolute("")
  byte-code(...)
  org-agenda-get-timestamps(nil)
  org-agenda-get-day-entries("~/emacs_org/mozilla/mozilla.org" (2 6
2013) :deadline :scheduled :timestamp :sexp)
  apply(org-agenda-get-day-entries "~/emacs_org/mozilla/mozilla.org"
(2 6 2013) (:deadline :scheduled :timestamp :sexp))
  byte-code(...)
  byte-code(...)
  org-agenda-list(nil)
  call-interactively(org-agenda-list)
  byte-code(...)
  org-agenda(nil)
  call-interactively(org-agenda nil nil)

It's dying when it hits a headline as follows:

* Meeting 13:30
, <%%(memq (calendar-day-of-week date) '(3))>

I'm guessing this has something to do with the agenda sorting updates
in the commit not liking the fact that the sexp evaluates to true. If
the sexp evaluates nil for the day the agenda is trying to parse,
nothing happens. If it evaluates to something other than nil (t if I
use (= 3 (calendar-day-of-week date)), 3 if I use memq on a wednesday,
etc...), I get the above error.