problem compiling X11 ports under 9.1-RELEASE

[Will Parsons]

I've recently installed 9.1-RELEASE on a laptop and am in the process
of installing the ports that I want.  On several now, I've encountered
error messages that I don't know how to deal with and for which I
don't see anything in the UPDATING file that seems to be relevant.
For example, trying to build both graphics/xv and x11-clocks/wmclock
results failure with the primary error message being:

imake -DUseInstalled -I/usr/local/lib/X11/config
Imakefile.c:16: error: Imake.tmpl: No such file or directory

followed by:

make: don't know how to make all. Stop

This happens both using portmaster (my usual method of installing
ports) and installing manually (cd /usr/ports/x/y; make).

Imake seems to be installed (pkg_version reports imake-1.0.4,1) so I
don't know where to go from here.