dpkg-deb: Add epoch when needed to built package names

The upstream part of the version can already contain colons, so there's
no reason not to add it for the epoch, and this allows to store on the
same directory packages with same version but different epoch.

Closes: #551323

debian/changelog

@@ -27,6 +27,8 @@ dpkg (1.16.3) UNRELEASED; urgency=low
     current locale (although this was only affecting the old deb format).
   * Ignore the minor format version number for deb-split format, unifying
     the behaviour with the deb format.
+  * Add epoch when needed to package names generated by dpkg-deb.
+    Closes: #551323
 
   [ Helge Kreutzmann ]
   * Fix a typo in man/dpkg-buildflags.1.

dpkg-deb/build.c

@@ -373,7 +373,7 @@ pkg_get_pathname(const char *dir, struct pkginfo *pkg)
   char *path;
   const char *versionstring, *arch_sep;
 
-  versionstring = versiondescribe(&pkg->available.version, vdew_never);
+  versionstring = versiondescribe(&pkg->available.version, vdew_nonambig);
   arch_sep = pkg->available.arch->type == arch_none ? "" : "_";
   m_asprintf(&path, "%s/%s_%s%s%s%s", dir, pkg->set->name, versionstring,
              arch_sep, pkg->available.arch->name, DEBEXT);