babel: fixes for commit 08e2596

* lisp/ob-core.el (org-babel-graphical-output-file): Use `user-error'
instead of `error'.

* lisp/ob-maxima.el (org-babel-execute:maxima, org-babel-maxima-expand):
* lisp/ob-octave.el (org-babel-execute:octave): Guard
`org-babel-graphical-output-file' with `ignore-errors'.
ox-latex: Fix export of inlinetasks with empty contents

* lisp/ox-latex.el (org-latex-inlinetask): Skip body if contents are
  empty.

Thanks to Michael Weylandt for reporting it and providing
a preliminary patch.
http://permalink.gmane.org/gmane.emacs.orgmode/86384
Merge branch 'maint'