Enabling fetch.type svn to work with a proxy

[Blair Zajac]

I'm trying to install netpbm from behind a firewall and it isn't working 
because 'fetch.type svn' doesn't honor http_proxy.

Newer svn versions support the following:

$ svn co \
   --config-option servers:global:http-proxy-host=PROXY.MYDOMAIN.COM \
   --config-option servers:global:http-proxy-port=8080

I'd like to add this to Tcl/port1.0/portfetch.tcl.  Being a coder but 
not a Tcl coder, how do I check if http_proxy is set in portfetch.tcl 
and get that to svn's command line?  Right now, I am unable to see the 
http_proxy variable in portfetch.tcl

BTW, this seems better than adding a directory with a svn config file 
and passing --config-dir to svn.

Thanks,
Blair