So far we have discovered the line
local proto=$(echo $netfile | sed 's|://.*||')
from get_downloadclient() should be replced with
local proto=$(echo "$url" | sed 's|://.*||')

Also,
local dlcmd=$(echo "$dlagent" | sed "s|%o|$file.part|" | sed "s|%u|$netfile|"
from get_downloadcmd() fails due to sed's handling of & in the rhs of the expression.

I locally made the change to get_downloadclient()

the cl-asdf package in AUR (http://aur.archlinux.org/packages.php?do_Details=1&ID=18800&O=&L=&C=&K=&SB=&SO=&PP=&do_Orphans=&SeB=) mysteriously fails.

The makepkg line that fails is '$(get_downloadcmd "$dlclient" "$netfile" "$file") || ret=$?'. The "get_downloadcmd()" routine works fine (calling it by itself echoes a command which I can run in an interactive bash session with no errors), but somehow the line as a whole manages to fail with this message: "/usr/bin/wget: option requires an argument -- 'O'".

FYI, the output of get_downloadcmd() for this specific package is: '/usr/bin/wget -c -t 3 --waitretry=3 -O asdf.lisp?revision=1.123.part http://cclan.cvs.sourceforge.net/*checkout*/cclan/asdf/asdf.lisp?revision=1.123';

I also suffer from this bug in my ut PKGBUILD (http://aur.archlinux.org/packages.php?ID=15763). I cannot download from the original site (http://www.liflg.org/?what=dl&catid=6&gameid=51&filename=unreal.tournament_436-multilanguage.run). I have to rely on unreliable mirrors instead.

What makepkg (from pacman 3.2.0-1) tells me (after I put the URL in single quotes):

% makepkg -sfic
==> Making package: ut 451-4 i686 (Sun Aug 3 22:04:14 CEST 2008)
==> Checking Runtime Dependencies...
==> Checking Buildtime Dependencies...
==> Retrieving Sources...
==> ERROR: There is no agent set up to handle URLs. Check /etc/makepkg.conf.
Aborting...
-> Downloading ?what=dl&catid=6&gameid=51&filename=unreal.tournament_436-multilanguage.run...
==> ERROR: There is no agent set up to handle URLs. Check /etc/makepkg.conf.
Aborting...
-> Downloading ?what=dl&catid=6&gameid=51&filename=unreal.tournament_436-multilanguage.goty.run...
-> Using cached copy of UTPGPatch451.tar.bz2
-> Found ut.desktop in build dir
-> Found base.list in build dir
==> WARNING: Integrity checks (md5) are missing or incomplete.
==> Extracting Sources...
==> ERROR: Unable to find source file ?what=dl&catid=6&gameid=51&filename=unreal.tournament_436-multilanguage.run for extraction.
Aborting...

The patch can also be found here : http://shining.toofishes.net/gitweb/gitweb.cgi?p=pacman.git;a=shortlog;h=refs/heads/makepkg

I tested ut and cl-atse with it and it worked fine.

However, the filename is awful with these stupid urls (?what=dl&catid=6&gameid=51&filename=unreal.tournament_436-multilanguage.run and asdf.lisp?revision=1.123), but well, it has always been like that.

Hooray it works!

Thanks Xavier, I did not know about nullglob. Now I know why they call you "veteran programmer extraordinaire" :)

Look at the log at the beginning how the patch, I gave proper credits there :
"Thanks to Henning Garus for pointing out that nullglob was problematic with
urls containing expansion char like '?'."

http://archlinux.org/pipermail/pacman-dev/2008-July/012715.html

So I guess Henning Garus aka Gars deserves that title more than me :)