Fix whitespace issues found by git diff --check, add gitattributes

Set per file type attributes in .gitattributes to fine-tune whitespace
checks.  With the associated cleanups, the tree is now clean for git

doc/src/sgml/ref/select.sgml

@@ -376,7 +376,7 @@ TABLE [ ONLY ] <replaceable class="parameter">table_name</replaceable> [ * ]
         For example:
 <programlisting>
 SELECT * FROM unnest(ARRAY['a','b','c','d','e','f']) WITH ORDINALITY;
- unnest | ordinality 
+ unnest | ordinality
 --------+----------
  a      |        1
  b      |        2