allow for beamer overlays even with noamsthm

[mbertucci47]

Right now the only thing keythms-beamer-support.tex does if noamsthm is loaded is disable \listofkeytheorems.

\documentclass[noamsthm]{beamer}

\usepackage{keytheorems}

\newkeytheorem{theorem}

\begin{document}

\begin{frame}

\begin{theorem}
Some theorem
\end{theorem}

\begin{theorem}<2>
Another theorem
\end{theorem}

\end{frame}

\end{document}