mq: pop correct patches when changing pushable-ness of already applied ones

Before this patch, "hg qselect" with --pop/--reapply may pop incorrect
patches, because the index in "applied patches" is used to pop patches
by "mq.pop()", even though the index in "the series" should be used.

For example, when the already applied patch becomes guarded and it
follows the already guarded (= not yet applied) one, "hg qselect" is
aborted, because it tries to pop to guarded one.

This patch uses "mq.applied[i - 1].name" to pop to the patch, of which
the index in the "applied ones" is "i - 1".

hgext/mq.py

@@ -3026,7 +3026,7 b' def select(ui, repo, *args, **opts):'
                 if i == 0:
                     q.pop(repo, all=True)
                 else:
-                    q.pop(repo, str(i - 1))
+                    q.pop(repo, q.applied[i - 1].name)
                 break
     if popped:
         try:

tests/test-mq-guards.t

@@ -541,3 +541,28 b' test that qselect shows "number of guard'
   guards deactivated
   $ hg qselect not-new not-c not-d
   number of guarded, applied patches has changed from 0 to 1
+
+test that "qselect --reapply" reapplies patches successfully when the
+already applied patch becomes unguarded and it follows the already
+guarded (= not yet applied) one.
+
+  $ hg qpop -q -a
+  patch queue now empty
+  $ hg qselect not-new not-c
+  number of unguarded, unapplied patches has changed from 1 to 2
+  $ hg qpush -q -a
+  patch d.patch is empty
+  now at: b.patch
+  $ hg qapplied -v
+  0 G new.patch
+  1 G c.patch
+  2 A d.patch
+  3 A b.patch
+  $ hg qselect -q --reapply not-c not-b
+  now at: d.patch
+  cannot push 'b.patch' - guarded by '-not-b'
+  $ hg qseries -v
+  0 U new.patch
+  1 G c.patch
+  2 A d.patch
+  3 G b.patch