d/control: Make php packages cross-installable to i386.

Drop sed dependency for php-common. sed is already in build-essential on
i386, and the versioned dependency (>= 4.1.1-1) is obsolete.

Make php-common "Multi-Arch: foreign" to indicate it has no dependencies
on architecture-dependent packages.

debian/control

@@ -128,9 +128,9 @@ Description: command-line interpreter for the PHP scripting language (default)
 
 Package: php-common
 Architecture: all
+Multi-Arch: foreign
 Section: php
 Depends: psmisc (>= 22.15-1~),
-         sed (>= 4.1.1-1),
          ${misc:Depends}
 Breaks: php-amqp (<< 1.7.0~alpha2-4~),
         php-apcu (<< 5.1.3+4.0.10-2~),