Most of the time, there will be no discreprancy between programPath and
readProgramFile.
But, the programFile might have been written by an old version of git-annex
that is still installed, while a newer one is currently running. In this
case, we want to run the same one that's currently running.
This is especially important for things like the GIT_SSH=git-annex used for
ssh connection caching.
The only code that still uses readProgramFile directly is the upgrade code,
which needs to know where the standalone git-annex was installed, in order to
upgrade it.
The ctrl-c hack used before didn't actually seem to work.
No haskell libraries expose TerminateProcess. I tried just calling it via
FFI, but got segfaults, probably to do with the wacky process handle not
being managed correctly. Moving it all into one C function worked.
This was hell. The EvilLinker hack was just final icing on the cake.
We all know what the cake was made of.
Fixed up a number of things that had worked around there not being a way to
get that.
Most notably, transfer info files on windows now include the process id,
since no locking is currently done. This means the file format varies
between windows and unix.
