u-a: Move alternative temporary extension to the build system

This removes another dpkg-specific string from the code to make life
easier for downstreams using update-alternatives on non-dpkg based
systems.

debian/changelog

@@ -29,6 +29,8 @@ dpkg (1.18.5) UNRELEASED; urgency=medium
   * Portability:
     - Move DPKG_ADMINDIR environment variable name out from update-alternatives
       code, to make life easier for non-dpkg-based systems.
+    - Move alternatives temporary extension out from update-alternatives code,
+      to make life easier for non-dpkg-based systems.
   * Perl modules:
     - Add new CTRL_REPO_RELEASE control block type to Dpkg::Control.
     - Add new CTRL_COPYRIGHT_HEADER, CTRL_COPYRIGHT_FILES and

utils/Makefile.am

@@ -25,6 +25,7 @@ update_alternatives_SOURCES = \
 	update-alternatives.c
 
 update_alternatives_CPPFLAGS = \
+	-DALT_TMP_EXT=\".dpkg-tmp\" \
 	-DADMINDIR_ENVVAR=\"DPKG_ADMINDIR\" \
 	$(AM_CPPFLAGS)
 

utils/update-alternatives.c

@@ -63,8 +63,6 @@ static int opt_skip_auto = 0;
 static int opt_verbose = 0;
 static int opt_force = 0;
 
-#define ALT_TMP_EXT ".dpkg-tmp"
-
 /*
  * Functions.
  */