emptytemplate as new keyword in mapfile

[silke@…]

Instead of only returning a static html-page by the empty-tag in the
mapfile we often would like to return a template where some query 
specific information such as the coordinates of the query etc. can 
be filled in.

We therefor added the keyword "emptytemplate" to the mapfile.
It can be defined in the WEB object. Such you can specify a template 
which will be returned when the query has no results.

We are working quite a while with this enhancement and would like to 
see it in the main mapserver code. So it would be nice if you could 
have a look on it and submit it into cvs if appropriate. The patch 
on [1] is based on mapserver 4.2.3 since this is the version I am 
currently working on.