Revert "dpkg-deb: don't warn on unknown fields starting with "X-""

This reverts commit 66835c07b3eb5c6a5a1374e60e93dfaf12538323.

Conflicts:

	debian/changelog

debian/changelog

@@ -45,9 +45,6 @@ dpkg (1.15.1) UNRELEASED; urgency=low
     Thanks to Bill Allombert for the patch.
   * dpkg now correctly refuses empty parameters when an integer value is
     wanted. Closes: #386197 Based on a patch by Bill Allombert.
-  * dpkg-deb doesn't warn anymore when it encounters unknown DEBIAN/control
-    fields starting with "X-". Closes: #353040
-    Thanks to Nils Rennebarth for the patch.
   * Fix a mistake in the french translation of dpkg's manual page.
     Thanks to Jonathan Gibert. Closes: #522032
   * Fix dpkg-source to not die when uncompressor processes are killed by

dpkg-deb/build.c

@@ -73,9 +73,6 @@ static const char *arbitrary_fields[] = {
 static int known_arbitrary_field(const struct arbitraryfield *field) {
   const char **known;
 
-  /* always accept fields starting with x- */
-  if (strncasecmp(field->name, "x-", 2) == 0)
-    return 1;
   for (known= arbitrary_fields; *known; known++)
     if (strcasecmp(field->name, *known) == 0)
       return 1;