lint: Check whitespace rules in markdown files too.

tools/lint-all

@@ -43,10 +43,12 @@ api/setup.py
 api/integrations/perforce/git_p4.py
 puppet/apt/.forge-release
 puppet/puppet-common/tests/
+puppet/apt/README.md
 """.split()
 
 by_lang = lister.list_files(args, modified_only=options.modified, use_shebang=True,
-    ftypes=['py', 'sh', 'js', 'pp', 'css', 'handlebars', 'html', 'json'], group_by_ftype=True, exclude=exclude)
+    ftypes=['py', 'sh', 'js', 'pp', 'css', 'handlebars', 'html', 'json', 'md'],
+    group_by_ftype=True, exclude=exclude)
 
 # Invoke the appropriate lint checker for each language,
 # and also check files for extra whitespace.
@@ -154,6 +156,7 @@ css_rules = [
 handlebars_rules = whitespace_rules
 html_rules = whitespace_rules
 json_rules = [] # just fix newlines at ends of files
+markdown_rules = whitespace_rules
 
 def check_custom_checks():
     failed = False
@@ -186,6 +189,10 @@ def check_custom_checks():
         if custom_check_file(fn, json_rules):
             failed = True
 
+    for fn in by_lang['md']:
+        if custom_check_file(fn, markdown_rules):
+            failed = True
+
     return failed
 
 lint_functions = {}