configure: Drop AC_PREREQ back down to 2.62
configure: Drop AC_PREREQ back down to 2.62

Commit 39f57407639b85c7e929d349ee95eabc46d083e bumped the
autoconf version to 2.64 with no explicit rationale.  It looks
to me like a copy-and-paste error.  Reverting back to 2.62 (the
previous version).  2.63 at least (RHEL6) works here.

jigpu/gtk,bratsche/gtk-,jadahl/gtk,davidt/gtk,Distrotech/gtk2,davidgumberg/gtk,Distrotech/gtk2,Distrotech/gtk2,chergert/gtk,grubersjoe/adwaita,chergert/gtk,bratsche/gtk-,Distrotech/gtk2,simokivimaki/gtk,jadahl/gtk,bratsche/gtk-,chergert/gtk,Distrotech/gtk2,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,davidgumberg/gtk,jadahl/gtk,jigpu/gtk,Adamovskiy/gtk,jigpu/gtk,davidgumberg/gtk,msteinert/gtk,jessevdk/gtk,grubersjoe/adwaita,Adamovskiy/gtk,grubersjoe/adwaita,ebassi/gtk,davidgumberg/gtk,Lyude/gtk-,Distrotech/gtk2,simokivimaki/gtk,simokivimaki/gtk,grubersjoe/adwaita,Lyude/gtk-,Adamovskiy/gtk,msteinert/gtk,alexlarsson/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,alexlarsson/gtk,davidt/gtk,ebassi/gtk,msteinert/gtk,chergert/gtk,Lyude/gtk-,jessevdk/gtk,ebassi/gtk,ebassi/gtk,alexlarsson/gtk,simokivimaki/gtk,ahodesuka/gtk,jessevdk/gtk,alexlarsson/gtk,Adamovskiy/gtk,jadahl/gtk,davidt/gtk,alexlarsson/gtk,jigpu/gtk,chergert/gtk,Lyude/gtk-,davidgumberg/gtk,jadahl/gtk,Adamovskiy/gtk,chergert/gtk,msteinert/gtk,bratsche/gtk-,jigpu/gtk,simokivimaki/gtk,Sidnioulz/SandboxGtk,davidt/gtk,ahodesuka/gtk,grubersjoe/adwaita,Sidnioulz/SandboxGtk,ebassi/gtk,simokivimaki/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,Adamovskiy/gtk,ahodesuka/gtk,davidgumberg/gtk,jessevdk/gtk,davidt/gtk,bratsche/gtk-,Adamovskiy/gtk,Lyude/gtk-,jigpu/gtk,ahodesuka/gtk,Sidnioulz/SandboxGtk,Adamovskiy/gtk,ahodesuka/gtk,Lyude/gtk-,ahodesuka/gtk,ahodesuka/gtk,davidt/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,grubersjoe/adwaita,alexlarsson/gtk,grubersjoe/adwaita,chergert/gtk,msteinert/gtk,jadahl/gtk,alexlarsson/gtk,davidgumberg/gtk,jessevdk/gtk,grubersjoe/adwaita,bratsche/gtk-,Lyude/gtk-,jessevdk/gtk,ahodesuka/gtk,chergert/gtk,ebassi/gtk,jessevdk/gtk,msteinert/gtk