Replace uses of rb_cvar_set/get with rb_cv_set/get. The rb_cv_*** functions don't change signatures between 1.8 and 1.9.
Replace uses of rb_cvar_set/get with rb_cv_set/get. The rb_cv_*** functions don't change signatures between 1.8 and 1.9.

Fix tmp file leak if Montage#texture= called more than once.

jonmartindell/rmagick,rmagick-temp/rmagick,modulexcite/rmagick,prognostikos/rmagick,tvon/rmagick,btakita/rmagick,btakita/rmagick,antonifs/rmagick,pecha7x/rmagick,modulexcite/rmagick,prognostikos/rmagick,rmagick-temp/rmagick,chand3040/Rmagic,tvon/rmagick,btakita/rmagick,pecha7x/rmagick,rmagick/rmagick,carsonreinke/rmagick,chand3040/Rmagic,mockdeep/rmagick,mockdeep/rmagick,prognostikos/rmagick,rmagick/rmagick,apecherin/rmagick,tvon/rmagick,carsonreinke/rmagick,rmagick/rmagick,carsonreinke/rmagick,mockdeep/rmagick,apecherin/rmagick,jonmartindell/rmagick,rmagick-temp/rmagick,mockdeep/rmagick,chand3040/Rmagic,antonifs/rmagick,jonmartindell/rmagick,antonifs/rmagick