solaris: tests can't use tail -n

Solaris tail doesn't recognize the -n option.  Replace the one use of it
with some inline python code, and add a test case to check-code.py.

contrib/check-code.py

@@ -67,6 +67,7 b' testpats = ['
     (r'echo -n', "don't use 'echo -n', use printf"),
     (r'(^| )wc[^|]*$\n(?!.*\(re\))', "filter wc output"),
     (r'head -c', "don't use 'head -c', use 'dd'"),
+    (r'tail -n', "don't use the '-n' option to tail, just use '-<num>'"),
     (r'sha1sum', "don't use sha1sum, use $TESTDIR/md5sum.py"),
     (r'ls.*-\w*R', "don't use 'ls -R', use 'find'"),
     (r'printf.*[^\\]\\([1-9]|0\d)', "don't use 'printf \NNN', use Python"),

tests/test-import-merge.t

@@ -129,7 +129,9 b" Test that --exact on a bad header doesn'"
   $ echo a>>a
   $ hg ci -m3
   $ hg export 2 | head -7 > ../a.patch
-  $ hg export tip | tail -n +8 >> ../a.patch
+  $ hg export tip > out
+  >>> apatch = open("../a.patch", "a")
+  >>> apatch.write("".join(open("out").readlines()[7:]))
 
   $ cd ..
   $ hg clone -qr0 repo3 repo3-clone