check-code: expand sed rule to include more offenders

Expands the rule added in 5e4491c114b2 to include cases where the
address is a line number instead of a regular expression, and fixes an
instance of this pattern in test-unionrepo.t.

contrib/check-code.py

@@ -74,7 +74,7 b' testpats = ['
     (r'/dev/u?random', "don't use entropy, use /dev/zero"),
     (r'do\s*true;\s*done', "don't use true as loop body, use sleep 0"),
     (r'^( *)\t', "don't use tabs to indent"),
-    (r'sed .*\'/[^/]*/i[^\\][^\n]',
+    (r'sed .*\'(\d+|/[^/]*/)i[^\\][^\n]',
      "put a backslash-escaped newline after sed 'i' command"),
   ],
   # warnings

tests/test-unionrepo.t

@@ -25,7 +25,8 b' Create one repository'
   $ hg clone -q repo1 --rev 0 repo2
   $ cd repo2
   $ touch repo2-1
-  $ sed '1irepo2-1 at top' f > f.tmp
+  $ sed '1i\
+  > repo2-1 at top' f > f.tmp
   $ mv f.tmp f
   $ hg ci -Aqmrepo2-1
   $ touch repo2-2