HTTP/FTP Downloads (again)

[Tony J. White]

https://bugzilla.icculus.org/show_bug.cgi?id=2661#c20

I've made some cvar related changes to the cURL support patch.

To review, the ET look-alike cvars for this have been dropped in an effort
to make the impact on SERVERINFO string much smaller.

The new server cvars for controlling this feature are:

sv_allowDownload [integer]
	This cvar already exists in SERVERINFO and previously the only values
        recognized were either 0 (off) non-0 (on).  Now this is a bit-flag
	value with any of the following combinations

	1 - traditional UDP downloading allowed
	2 - download redirection allowed (cURL)
	4 - client should disconnect when using download redirection

	This makes the only valid settings:
	 0 - no downloads
	 1 - udp downloads only
	 2 - redirected downloads only
	 3 - either udp or redirected downloads allowed
         6 - disconnected redirect downloads only
	 7 - udp download or disconnected redirect downloads

sv_dlURL [string]
	This used to be sv_wwwBaseURL in earlier patches.  A string that
	represents the base of the download URL.  For example, setting 
	this to "http://tjw.org" may try to download a pak 
	at "http://tjw.org/baseq3/test.pk3"

I will be testing this latest patch the three main platforms.  If
all goes well in testing and nobody has any concerns about this patch I
will commit it to trunk.

-Tony