Unwanted axis labels when rug() has POSIXlt argument (PR#10380)

rug() may add integer axis labels when called with a POSIXlt object
as argument.

dtimes <- c("09/29/2007  12:54", "09/30/2007  00:14", "10/01/2007   
00:14",
               "10/02/2007  00:14", "10/03/2007  00:14", "10/04/2007   
00:14",
               "10/05/2007  00:14", "10/06/2007  00:14", "10/07/2007   
00:14",
               "10/08/2007  00:14")
z <- strptime(dtimes, "%m/%d/%Y %H:%M", tz="EST5EDT")
plot(z, rnorm(10))
rug(z)

This happens also undo Windows, both with 2.6.0 and 2.7.0 (2007-10-26  
r43284)

--please do not edit the information below--

Version:
platform = i386-apple-darwin8.10.1
arch = i386
os = darwin8.10.1
system = i386, darwin8.10.1
status =
major = 2
minor = 6.0
year = 2007
month = 10
day = 03
svn rev = 43063
language = R
version.string = R version 2.6.0 (2007-10-03)

Locale:
C

Search Path:
.GlobalEnv, package:stats, package:graphics, package:grDevices,  
package:utils, package:datasets, package:methods, Autoloads,  
package:base

John Maindonald             email: john.maindonald at anu.edu.au
phone : +61 2 (6125)3473    fax  : +61 2(6125)5549
Centre for Mathematics & Its Applications, Room 1194,
John Dedman Mathematical Sciences Building (Building 27)
Australian National University, Canberra ACT 0200.