ox-latex: Remove unwanted indentation in horizontal rules

* lisp/ox-latex.el (org-latex-horizontal-rule): Add "\noindent" macro
  before the horizontal rule.

Reported-by: Justen Rickert <justenrickert@gmail.com>
<http://permalink.gmane.org/gmane.emacs.orgmode/113092>

lisp/ox-latex.el

@@ -2052,8 +2052,8 @@ CONTENTS is nil.  INFO is a plist holding contextual information."
        "\n")
      (org-latex--wrap-label
       horizontal-rule
-      (format "\\rule{%s}{%s}"
-	      (or (plist-get attr :width) "\\linewidth")
+      (format "\\noindent\\rule{%s}{%s}"
+	      (or (plist-get attr :width) "\\textwidth")
 	      (or (plist-get attr :thickness) "0.5pt"))
       info))))