using C++ memory managment for arrays

there's still a crasher-bug when PBuffer is called
initialize glSelectBuffer-length to 0

rather than "-1", as the latter makes comparision with signed ints buggy.

This fixes a crasher bug
properly initialize buffer/size

Fixes another crasher
only call glSelectBuffer if we actually have a buffer
fix memleak
pass full Pd to gemstate_run
don't check for GLEW_framebuffer_object on destroyFBO

we only destroy ressources that have been successfully created.
they only have been successfully created, if the necessary
openGL-extension have been available.