### Please describe the problem.

git uses environment variable GIT_SSH to determine SSH client.

I set it to plink.exe because I extensively use pageant infrastructure and do NOT want to have 2 systems lying around.

Unfortunately git-annex seems to ignore that.

Even worse, it results in unpredicted behavior because the git part works (e.g. clone) whereas annex/rsync does not resulting in half-ok repositories without meaningful error messages.

It only becomes evident when ssh.exe in the git repository is deleted.

### What steps will reproduce the problem?

Set %GIT_SSH% and remove ssh.exe

You will get

     git-annex: ssh: createProcess: does not exist (No such file or directory)
     failed
     git-annex: drop: 1 failed

### What version of git-annex are you using? On what operating system?

Windows 8,

     $ git annex version
     git-annex version: 5.20140411-gda795e0
     build flags: Assistant Webapp Webapp-secure Pairing Testsuite S3 WebDAV DNS Feeds Quvi TDFA CryptoHash
     key/value backends: SHA256E SHA1E SHA512E SHA224E SHA384E SKEIN256E SKEIN512E SHA256 SHA1 SHA512 SHA224 SHA384 SKEIN256 SKEIN512 WORM URL
     remote types: git gcrypt S3 bup directory rsync web webdav tahoe glacier hook external
     local repository version: 5
     supported repository version: 5
     upgrade supported from repository versions: 2 3 4


### Please provide any additional information below.


