made cprogs.dat builtin #303 (setproperty) accept 1 parm, in this case it will return...

made cprogs.dat builtin #303 (setproperty) accept 1 parm, in this case it will return a value of property stored in engine struct instead of setting it. Pretty useful with several viewports code + 2d drawing. Curently the only property that can't be returned is VF_VIEWPORT (will give a warning) as it stored in 2 vectors (VF_MIN and VF_SIZE). To use new feature define 2 more builtins:
float(float property) getproperty = #303;
vector(float property) getpropertyvec = #303;

git-svn-id: svn://svn.icculus.org/twilight/trunk/darkplaces@10197 d7cf8633-e32d-0410-b094-e92efae38249
::stable-branch::merge=515c01976be481f5d06169f193a7527fd567e83c