BUNDLE_RESOURCE_FILES problem keeping subdirectories

[Sebastian Reitenbach]

I played a bit with Germans silver theme, in order to 
get it installing properly into the system Themes directory.

I added the following to the GNUmakefile:

$(BUNDLE_NAME)_RESOURCE_FILES = Resources/Silver.tiff \
                                $(wildcard Resources/*.clr) \
                                $(wildcard Resources/ThemeImages/*.tiff) \
                                $(wildcard Resources/ThemeTiles/*.tiff)

It picks up all the files from the Resources directory, and also
from its subdirectories, but it places everything plain into
the Resources directory in the installation path. 

i.e. Resources/ThemImages/blah.tiff goes into
/usr/local/lib/GNUstep/Themes/Silver.theme/Resources/blah.tiff
instead of the wanted
/usr/local/lib/GNUstep/Themes/Silver.theme/Resources/ThemeImages/blah.tiff

is there an easy way to keep the directory structure for the resources
without overriding the install target or adding a post-install target?

Sebastian