check-code: detect "% inside _()" when there are leading whitespaces

Before this patch, "contrib/check-code.py" can't detect "% inside _()"
correctly, when there are leading whitespaces before the format
string, like below:

    _(
      "format string %s" % v)

This patch adds regexp pattern "[ \t\n]*" before the pattern matching
against the format string.

"[\s\n]" can't be used in this purpose, because "\s" is automatically
replaced with "[ \t]" by "_preparepats()" and "\s" in "[]" causes
nested "[]" unexpectedly.

contrib/check-code.py

@@ -207,8 +207,8 b' pypats = ['
     (r'\s<>\s', '<> operator is not available in Python 3+, use !='),
     (r'^\s*\t', "don't use tabs"),
     (r'\S;\s*\n', "semicolon"),
-    (r'[^_]_\((?:"[^"]+"[ \t\n+]*)+%', "don't use % inside _()"),
-    (r"[^_]_\((?:'[^']+'[ \t\n+]*)+%", "don't use % inside _()"),
+    (r'[^_]_\([ \t\n]*(?:"[^"]+"[ \t\n+]*)+%', "don't use % inside _()"),
+    (r"[^_]_\([ \t\n]*(?:'[^']+'[ \t\n+]*)+%", "don't use % inside _()"),
     (r'(\w|\)),\w', "missing whitespace after ,"),
     (r'(\w|\))[+/*\-<>]\w', "missing whitespace in expression"),
     (r'^\s+(\w|\.)+=\w[^,()\n]*$', "missing whitespace in assignment"),

tests/test-check-code.t

@@ -255,3 +255,32 b''
    warning: add two newlines after '.. note::'
   [1]
 
+  $ cat > ./map-inside-gettext.py <<EOF
+  > print _("map inside gettext %s" % v)
+  > 
+  > print _("concatenating " " by " " space %s" % v)
+  > print _("concatenating " + " by " + " '+' %s" % v)
+  > 
+  > print _("maping operation in different line %s"
+  >         % v)
+  > 
+  > print _(
+  >         "leading spaces inside of '(' %s" % v)
+  > EOF
+  $ "$check_code" ./map-inside-gettext.py
+  ./map-inside-gettext.py:1:
+   > print _("map inside gettext %s" % v)
+   don't use % inside _()
+  ./map-inside-gettext.py:3:
+   > print _("concatenating " " by " " space %s" % v)
+   don't use % inside _()
+  ./map-inside-gettext.py:4:
+   > print _("concatenating " + " by " + " '+' %s" % v)
+   don't use % inside _()
+  ./map-inside-gettext.py:6:
+   > print _("maping operation in different line %s"
+   don't use % inside _()
+  ./map-inside-gettext.py:9:
+   > print _(
+   don't use % inside _()
+  [1]