Several questions about beamer export

[Julien Cubizolles <j.cubizolles@free.fr>]

I'm trying to switch all my LaTeX needs to orgmode but I'm still
confused by several little things I could not understand in the
manual. I'm not sure what the policy is on the mailing-list, let me know
if it's best to split this message into several ones.

* What's the difference between BEAMER_ENV and BEAMER_env ?

* What is the best way to generate 
 \only<2-3>{Some text of picture} without creating a new heading ?

* Is there a shortcut/easy template to ATTR_BEAMER ? I know I could use
  a yas snippet but maybe there is already something in place.

* in LaTeX you can use \graphicspath to define the directories in which
  to look for picture files. Does org mode offer the same possibility ?

* All the headers I add end up on the same line when I define them like
  in the following (even with an empty line).

 #+LATEX_HEADER_EXTRA: \institute{My Institure}
  
 #+LATEX_HEADER:\usepackage{mypackage}

 The LaTeX file produced is not very readable. How can I produce
 linebreaks between different LATEX_HEADER entries ?

Julien.