ox-latex: Use "ulem" package for both underline and strike through

* lisp/org.el (org-latex-default-packages-alist): Load "ulem" package
  by default.  Use "[normalem]" option to preserve \emph definition.
* lisp/ox-latex.el (org-latex-text-markup-alist): Use "\uline" and
  "\sout" commands from "ulem" package.

lisp/org.el

@@ -3805,7 +3805,7 @@ header, or they will be appended."
     (""     "longtable" nil)
     (""     "float"     nil)
     (""     "wrapfig"   nil)
-    (""     "soul"      t)
+    ("normalem" "ulem"  t)
     (""     "textcomp"  t)
     (""     "marvosym"  t)
     (""     "wasysym"   t)
@@ -3828,7 +3828,7 @@ Org mode to function properly:
   symbols used for interpreting the entities in `org-entities'.
   You can skip some of these packages if you don't use any of the
   symbols in it.
-- soul: for underline and strike-through
+- ulem: for underline and strike-through
 - graphicx: for including images
 - float, wrapfig: for figure placement
 - longtable: for long tables

lisp/ox-latex.el

@@ -524,8 +524,8 @@ When nil, no transformation is made."
 (defcustom org-latex-text-markup-alist '((bold . "\\textbf{%s}")
 					 (code . verb)
 					 (italic . "\\emph{%s}")
-					 (strike-through . "\\st{%s}")
-					 (underline . "\\ul{%s}")
+					 (strike-through . "\\sout{%s}")
+					 (underline . "\\uline{%s}")
 					 (verbatim . protectedtexttt))
   "Alist of LaTeX expressions to convert text markup.