tests: invoke hg command indirectly from shell script to run on Windows

Before this patch, test-tag.t can't run successfully on Windows,
because:

  - quoted hg command ('"hg"') prevents "hg.bat" from working correctly
    (only at testing with pure Python build)

    "%~f0" and "%~dp0hg" in "hg.bat" cause unexpected result in this
    case. BTW, quoted "\path\to\hg" works correctly.

  - "`pwd`" in the command line is expanded unexpectedly

    not "C:\path\to\TESTTMP" but "C;C:\path\to\TESTTMP"

tests/test-tag.t

@@ -395,7 +395,10 b' commit hook on tag used to be run withou'
   $ hg -R repo-tag commit -A -m "test"
   adding test
   $ hg init repo-tag-target
-  $ hg -R repo-tag --config hooks.commit="\"hg\" push \"`pwd`/repo-tag-target\"" tag tag
+  $ cat > "$TESTTMP/issue3344.sh" <<EOF
+  > hg push "$TESTTMP/repo-tag-target"
+  > EOF
+  $ hg -R repo-tag --config hooks.commit="sh ../issue3344.sh" tag tag
   pushing to $TESTTMP/repo-tag-target (glob)
   searching for changes
   adding changesets