Ported from upstream by Dennis Schridde.

https://bugs.gentoo.org/show_bug.cgi?id=560654

https://bitbucket.org/rivanvx/beamer/issues/261/beamer-and-subcaption
https://sourceforge.net/p/latex-caption/tickets/21/
https://sourceforge.net/p/latex-caption/code/100/

Index: texmf-dist/tex/latex/caption/caption.sty
===================================================================
--- texmf-dist/tex/latex/caption/caption.sty	(revision 99)
+++ texmf-dist/tex/latex/caption/caption.sty	(revision 100)
@@ -36,7 +36,6 @@
 %% and the user manuals
 %%   caption-deu.tex, caption-eng.tex, and caption-rus.tex.
 %% 
- % bicaption.sty, ltcaption.sty, subcaption.sty, and newfloat.sty,
 \NeedsTeXFormat{LaTeX2e}[1994/12/01]
 \def\caption@tempa$Id: #1 #2 #3-#4-#5 #6${%
   \def\caption@tempa{#3/#4/#5 }\def\caption@tempb{#2 }}
@@ -379,6 +378,18 @@
       {\@dblarg{\@caption\@captype}}%
     }}%
   \caption@CheckCommand\caption{%
+    % beamerbaselocalstructure.sty, Joseph Wright committed 4ac715c 2013-09-04
+    \def\caption{%
+      \ifx\@captype\@undefined
+        \@latex@error{\noexpand\caption outside figure or table}\@ehd
+        \expandafter\@gobble
+      \else
+        \refstepcounter\@captype
+        \expandafter\@firstofone
+      \fi
+      {\@dblarg{\@caption\@captype}}%
+    }}%
+  \caption@CheckCommand\caption{%
     % float.sty [2001/11/08 v1.3d Float enhancements (AL)]
     \long\def\caption{%
       \ifx\@captype\@undefined