[PATCH] Makefile: add support for git svn clones

git has an interface for cloning SVN repositories into git
 which some users might decide to use. For those users' 
surprise, the repository will always fail to build on
svnonly target and it will exit early.

The problem is simple enough to fix by just checking if a
.git directory exists in top_builddir and, if so, call git
svn info insstead of svn info.

I think we are unlikely to accept this change.  Nobody in R
Core uses git this way, so it would never be tested, and
would likely soon fail.

it will be tested by anybody using git svn clone, right ?

Indeed, it already fails if someone were to try it on
Windows, since you didn't patch the makefiles for that
platform.

yeah, sorry about that, I wasn't aware there were
windows-specific Makefiles with duplicated logic in the
repository.

The R sources are kept in an SVN repository, and as long as 
that's true, we're only likely to support direct SVN access.

Fair enough. But don't you think it's a bit odd to couple the 
repository compilation with the availability of a specific SCM 
tool ?

I mean, R just won't build unless you have svn info available,
I think that's pretty odd. Printing a warning would be another
 possibility, but exitting build is almost an overreaction.

That's just false.  Build from a tarball, and you can store it
anyway you like.

I'm talking about the SVN repository. Building from a tarball
prevents me from tracking R's revisions, don't you think ? But as I
said, if the community doesn't want to support a git svn clone,
that's all fine and dandy.

So why not make your patch locally, and publish it for any other git
user to incorporate?  If some change to the master copy breaks it,

you'll see it, and you'll fix it.  Then everyone's happy.  One of the
purported advantages of git is the fact that it doesn't require a

central repository for everything.