Add frozen land texture

This change from r0cd63b963330 caused more troubles than solved. Also fix some warnings.

due to popular demand, add a compile time switch to manually select whether to build the internal physfs (default) or not

Add land freezing

Global notice with /global command. Can now warn users when doing server restart.

documentation

Oh, and # too to prevent occasional game hang when N is followed by #

perform a version check before including physfs (maybe there is a better place for this?) and allow overriding automagic search

Flush buffer on N command

disable unneeded physfs archives (as of bug #529)