bug#23249: 25.1.50; unexpected behavior marking paragraphs in latex-mode

[Mark Oteiza <mvoteiza@udel.edu>]

From -Q:

1. open a new buffer foo.tex
2. insert a commented line followed by an uncommented one; e.g.

% dog

cat

3. Put point at beginning of buffer
4. M-h

I would expect the line with "dog" to be marked, but instead, the lines
following are marked.  I see there is some history with the settings of
paragraph-start and paragraph-separate (Bug#5821 and friends), but the
current settings make movement around and uncommenting of commented blocks a
pain.

I can see part of paragraph-{start,separate} in latex-mode are to help
navigating around tex environments and things like that, but it's not
clear to me what further features are packed into the regexen.

In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, X toolkit, Xaw scroll bars)
 of 2016-03-20 built on logos
Repository revision: 5283593ced29a2c98e4af3607a68ee7a6d10fcac
Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --without-gconf --with-modules
 --with-x-toolkit=lucid 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe
 -fstack-protector-strong --param=ssp-buffer-size=4 -g
 -fvar-tracking-assignments -g -fvar-tracking-assignments'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro'