Docs: Fix breakage with Sphinx 1.5 and upper

Commit 85c21e5c (docs-rst: better adjust margins and font size) added a
\usepackage{geometry} that conflicts with another inclusion deep within the
dependencies with newer versions of Sphinx, causing the the PDF build to fail
with a "conflicting parameters" error.

Detect the Sphinx version, using sphinxsetup for Sphinx versions 1.5 and
upper.

Fixes: 85c21e5c
[jc: Tweaked logic to exclude 1.5.x for x < 3 ]
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>

Documentation/conf.py

@@ -271,8 +271,6 @@ latex_elements = {
 
 # Additional stuff for the LaTeX preamble.
     'preamble': '''
-	% Adjust margins
-	\\usepackage[margin=0.5in, top=1in, bottom=1in]{geometry}
         \\usepackage{ifthen}
 
         % Allow generate some pages in landscape
@@ -343,6 +341,12 @@ latex_elements = {
 if major == 1 and minor > 3:
     latex_elements['preamble']  += '\\renewcommand*{\\DUrole}[2]{ #2 }\n'
 
+if major == 1 and minor <= 4:
+    latex_elements['preamble']  += '\\usepackage[margin=0.5in, top=1in, bottom=1in]{geometry}'
+elif major == 1 and (minor > 5 or (minor == 5 and patch >= 3)):
+    latex_elements['sphinxsetup'] = 'hmargin=0.5in, vmargin=0.5in'
+
+
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title,
 #  author, documentclass [howto, manual, or own class]).