Make Cvar::Register return a bool for success.

The VM services would call Register on cvars given by the VM.
That call would fail for engine cvar names but the VM services
didn't know and would try deleting the cvars when the VM is
shutdown, removing the engine cvar.

Also we cannot simply use a Cvar::IsRegistered because in a
multithreaded environment it would be incorrect:
- VM service thread (checks if the VM can create the cvar):
    IsRegistered("foo") -> false
- Other Engine thread (for whatever reason):
    Register("foo", ...) // success
- VM service thread (thinks the VM can register the cvar):
    Register("foo", ...) // silent failure
Later...
- VM service thread (cleaning up VM cvars):
    Unregister("foo")
Try to order images loading by pak and then extension
Fix cleaning of in-game names ending with '^'
Small fixes to the C++ization of /map
Use Cmd::Args for client commands
Implement color reset string ^* in UI text drawing
Merge branch 'color_issue307' of github.com:slipher/Unvanquished

This fixes #307.
Always use WWW downloads.

cl_wwwDownload was only used to tell the server we were an old client.
The client didn't even check if it was on when the server sent
www download messages.
Remove unused (^C^V from Urban Terror?) defines
Remove the automatic "needhealth" vsay when trying to use an unavailable medkit.
Add an automatic vsay when throwing a grenade.
Synchronize player names in server with those in the game logic
Merge pull request #321 from slipher/gamename_issue316

This fixes #316.
Merge branch 'master' into librocket