Exclude .md files from version control conflict detection.

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 751ae525751be38445e4bca2fd0a02c0ac7dd03e..2e33261c5af23b65309a1febb899020cf05f7eda 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -841,6 +841,10 @@ def _CheckForVersionControlConflictsInFile(input_api, f):
   pattern = input_api.re.compile('^(?:<<<<<<<|>>>>>>>) |^=======$')
   errors = []
   for line_num, line in f.ChangedContents():
+    if f.LocalPath().endswith('.md'):
+      # First-level headers in markdown look a lot like version control
+      # conflict markers. http://daringfireball.net/projects/markdown/basics
+      continue
     if pattern.match(line):
       errors.append('    %s:%d %s' % (f.LocalPath(), line_num, line))
   return errors