Fix incorrect uninstallability counters caused by failed "easy" hints

When undoing the removal of a binary package by an "easy" hint, ensure
that the apt system is updated with the correct version of the package.

Signed-off-by: Adam D. Barratt <adam@adam-barratt.org.uk>

britney.py

@@ -2523,7 +2523,12 @@ class Britney:
                     if binary[0] == "-":
                         del self.binaries['testing'][arch][0][binary[1:]]
                         self.systems[arch].remove_binary(binary[1:])
-                    else: self.binaries['testing'][arch][0][binary] = undo['binaries'][p]
+                    else:
+                        binaries = self.binaries['testing'][arch][0]
+                        binaries[binary] = undo['binaries'][p]
+                        self.systems[arch].remove_binary(binary)
+                        self.systems[arch].add_binary(binary, binaries[binary][:PROVIDES] + \
+                            [", ".join(binaries[binary][PROVIDES]) or None])
 
             for (undo, pkg, pkg_name, suite) in lundo:
                 # undo the changes (virtual packages)