Don't start game entity loops at index 1

Skip all players or none.
Fix in g_svcmds.c copied from @exidl.
Add trap_FS_Tell to game and cgame VMs
Fix VM FOpenFile( FS_READ ) files seeking twice in FS_Seek
Remove unused variable baseOffset from fsh[]
Support FS_SEEK_END and negative offset for zipped files in FS_Seek

Use FS_SEEK_END in sound code instead of working around it.
If FS_SEEK_SET and going to current position, just return.
Try to protect FS VM syscalls from bad input
Remove old comment that FS_Seek doesn't work on zipped files
Remove function prototypes for non-existant Sys_* DLL functions
Store index of first free poly buffer instead of looping through them again

From ET:Legacy.

Note: poly buffers still don't render in Spearmint.
Remove redundent sets in cg_polybus.c
Merge remote-tracking branch 'spearmint/master'