opam: update to opam-1.2.0.beta4.

Using beta version to support OCaml 4.02.0, stable release should
follow soon.

srcpkgs/opam/template

@@ -1,15 +1,18 @@
 # Template file for 'opam'
 pkgname=opam
-version=1.1.1
-revision=2
+_version=1.2.0-beta4
+version=${_version/-/.}
+wrksrc=${pkgname}-${_version}
+revision=1
 build_style=gnu-configure
 disable_parallel_build=yes
-wrksrc=$pkgname-full-$version
-depends="ocaml curl"
-makedepends="ncurses-devel $depends"
+make_build_args="lib-ext all"
+depends="ocaml curl patch"
+makedepends="ncurses-devel ocaml curl"
 short_desc="OCaml package manager"
 maintainer="Christian Neukirchen <chneukirchen@gmail.com>"
 license="LGPL-3"
 homepage="http://opam.ocamlpro.com"
-distfiles="http://www.ocamlpro.com/pub/$pkgname-full-$version.tar.gz"
-checksum=bfcb78109cf88612b5170b25bb96aa576ed3908c8a68b9164a7ae16f9f59ae38
+distfiles="https://github.com/ocaml/${pkgname}/archive/${_version}.tar.gz"
+checksum=3c4029d7f3f528986d5f42e7ec5067f5dec16a793a2ea7438967b36f6c3c75ba
+nocross=yes