why we need these declarations sorted by version:
* dlopen() and dlsym() causes problems with GL sometimes.
  -> it would be nice if we'd be able to replace this
* using gl*() functions directly causes even more problems: system A
  compiles&&links boson but has GL version x, system B runs that binary, but has
  GL version y with x != y.
  -> we need to resolve functions on runtime, otherwise we may get
     * not support special features of system B, if y > x
     * not run at all, due to undefined references
* glXGetProcAddressARB() might be a way out of this problem (yet to be tested at
  this point!), but it does not guarantee that it returns NULL if a function is
  not available
  -> we need additional checks for the available functions (e.g. using
  glGetVersion() and/or by checking for the extensions)

this is what we need these files for.
