check-commit: make foo_bar naming regexp less greedy

\s is equivalent to the character class [ \t\n\r\f\v]. Using \s+ in
a regular expression against input with multiple lines may match across
multiple lines.

For the regexp in question, "\+\s+" would match "+\n " and similar
sequences, leading to false positives for functions that were included
in diff context, after a modified hunk.

contrib/check-commit

@@ -29,7 +29,7 b' errors = ['
     (r"^# .*\n.*\.\s+$", "don't add trailing period on summary line"),
     (r"^# .*\n.{78,}", "summary line too long (limit is 78)"),
     (r"^\+\n \n", "adds double empty line"),
-    (r"\+\s+def [a-z]+_[a-z]", "adds a function with foo_bar naming"),
+    (r"^\+[ \t]+def [a-z]+_[a-z]", "adds a function with foo_bar naming"),
 ]
 
 node = os.environ.get("HG_NODE")