build: Set DEFAULT_TEXT_DOMAIN to @PACKAGE@ for libdpkg

This makes sure the gettext() calls in the library code get the correct
domain name, otherwise if the program is using a domain other than
@PACKAGE@ (in this case dpkg), then it will not be able to find the
correct translations.

debian/changelog

@@ -87,6 +87,8 @@ dpkg (1.17.2) UNRELEASED; urgency=low
   * Fix crashes in the first call to gettext() after fork() on Mac OS X, by
     forcing the initialization at program start of the CoreFoundation cached
     values in libintl.
+  * Set a default gettext domain for libdpkg code, so that other programs
+    using a different domain can still get correct translations, like dselect.
 
   [ Updated programs translations ]
   * German (Sven Joachim).

lib/dpkg/Makefile.am

@@ -8,6 +8,7 @@ AM_CPPFLAGS = \
 	-DLOCALEDIR=\"$(localedir)\" \
 	-DCONFIGDIR=\"$(pkgconfdir)\" \
 	-DADMINDIR=\"$(admindir)\" \
+	-DDEFAULT_TEXT_DOMAIN=\"@PACKAGE@\" \
 	-idirafter $(top_srcdir)/lib/compat \
 	-I$(top_builddir) \
 	-I$(top_srcdir)/lib