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

src/backend/utils/misc/postgresql.conf.sample

@@ -370,12 +370,12 @@
 					#   panic
 
 #log_min_error_statement = error	# values in order of decreasing detail:
-				 	#   debug5
+					#   debug5
 					#   debug4
 					#   debug3
 					#   debug2
 					#   debug1
-				 	#   info
+					#   info
 					#   notice
 					#   warning
 					#   error