BUG #5981: Attempt to install language pltcl fails on 64-bit installation

The following bug has been logged online:

Bug reference:      5981
Logged by:          Chris Price
Email address:      cjprice@bigpond.net.au
PostgreSQL version: 9.0.3
Operating system:   Winders Server 2008 R2 Standard
Description:        Attempt to install language pltcl fails on 64-bit
installation
Details:

When I try to install the pltcl language on 64-bit Windows version of
PostreSQL (9.0.3) it fails with the following message:
ERROR: could not access file "$libdir/pltcl": No such file or directory
SQL state: 58P01

ActiveTcl is installed.
It works on a 32-bit installation of PostgreSQL.

I notice that the file pltcl.dll is not installed in the $libdir folder on
the 64-bit installation - is there a reason for this? Is the pltcl language
available on 64-bit installations on Windows?