Windows test suite fails the import/export tests.

It imports a file, but the worktree file remains a unlocked pointer
file. So the test fails. Running `git annex smudge--update` fixed the
file content. 

Reproduced outside the test suite, and tried with GIT_TRACE=1.
When `git-annex merge remote/master``runs git merge, it does then smudge
--clean the imported files. But smudge --update does not get run. The
post-merge hook should run it.

Ahh -- on windows, hooks are not written, because the code skips that
for a crippled filesystem, assuming it has no execute bit.

So, this is both a problem on windows and on crippled filesystems.
The user needs to run smudge --update themselves, or maybe git-annex
can do it sometimes. Eg, `git annex merge` (and sync) could certianly
smudge --update when on a crippled filesystem. And that would be
enough to fix the test suite.

But if a user is on a crippled filesystem with an adjusted branch, and
they do some other operation that would be covered by post-merge or
post-checkout hook, they will be surprised to find unpopulated pointer
files in the working tree.

I think this can be avoided. On eg fat on linux, all files are executable,
so the hook can be installed and will work. On Windows, a hook can start
with #!/bin/sh and not be executable, and will be run by the bash bundled
with git for windows.
--[[Joey]]

> [[fixed|done]]; 100% test pass on windows now --[[Joey]]
