meson.eclass: require at least meson-0.45.1

meson.eclass: require at least meson-0.45.1

Require newer meson in order to avoid build failures triggered
new meson is not installed soon enough. For example, I experienced
bug 649264 because I upgraded xorg-proto and libxshmfence packages
before meson.

Although meson-0.44.1 is enough to solve bug 649264, Mike Gilbert
suggests to require at least meson-0.45.1, since this version is
the latest stable on all archs.

Closes:	https://bugs.gentoo.org/649264
Reviewed-by: Mart Raudsepp <leio@gentoo.org>
Reviewed-by: Mike Gilbert <floppym@gentoo.org>