Beamer template: fix incompatibility of section slides with natbib.

Natbib (and presumably biblatex) bibliography commands create
their own section.  Since these are in frame environments,
we have an incompatibility with the `\AtBeginSection` macro
which creates a special frame when a new section occurs.
(We can't have a frame inside another frame.)

This change disables `\AtBeginSection` inside bibliography
slides.

Thinks to Yihui Xie for bringing the problem to my attention.
This supersedes #145.  See discussion there.

1 files changed, 15 insertions, 7 deletions

diff --git a/data/templates b/data/templates
-Subproject de2e524e7df0a9d4159f2794deaa2e1847c87d4
+Subproject a3c8439ad6e8d1da89be1069a9d62bedd62a327