Correct size and spacing of notes

This changeset resolves two issues with Beamer's notes command:
- The width of the notes page is based on a 4:3 aspect ratio (for a
  textwidth of 12cm) instead of being derived from the paper width.
- The baselineskip within notes varies by paragraph. Specifically, the
  first paragraph has tighter vertical spacing than subsequent
  paragraphs.
Beamer's beamer@outsideframenote macro is patched to correct both
issues.

Note: These changes should be contributed back to Beamer although the
second seems to be a known issue (https://goo.gl/qbPIYF).

slides/slides.dtx

@@ -377,5 +377,44 @@
 % }
 % \end{macro}
 %
+% \subsection*{Beamer Internals}
+%
+% \begin{macro}{beamer@outsideframenote}
+% Patch the \mintinline{latex}{note} macro to correct the text width for different aspect ratios.
+%    \begin{macrocode}
+\xpatchcmd{\beamer@outsideframenote}
+    {\textwidth=10.8cm}
+    {\textwidth=\dimexpr\paperwidth - (\Gm@lmargin + \Gm@rmargin)}
+    {%
+      \PackageInfo{slides}{%
+        Successfully patched textwidth in beamer@outsideframenote%
+      }%
+    }%
+    {%
+      \PackageWarning{slides}{%
+        Error patching beamer@outsideframenote; textwidth may be incorrect%
+      }%
+    }%
+%    \end{macrocode}
+%    \begin{macrocode}
+\xpatchcmd{\beamer@outsideframenote}
+    {\beamer@noteenvstart#2\beamer@noteenvend}
+    {\beamer@noteenvstart#2\par\beamer@noteenvend}
+    {%
+      \PackageInfo{slides}{%
+        Successfully patched beamer@outsideframenote to correct baselineskip%
+      }%
+    }%
+    {%
+      \PackageWarning{slides}{%
+        Error patching beamer@outsideframenote; baselineskip may be incorrect%
+      }%
+    }%
+%    \end{macrocode}
+% \changes{0.3.0}{2017/03/09}{
+%   Patch \texttt{beamer@outsideframenote} command
+% }
+% \end{macro}
+%
 % \Finale
 \endinput