"make test" fails if /path/to/git.git contains spaces

[Adam Roben <aroben@apple.com>]

I've noticed that "make test" fails if /path/to/git.git contains spaces, 
with the following error:

> $ make test
> make -C t/ all
> make[1]: Entering directory `/home/Adam Roben/dev/git/t'
> *** t0000-basic.sh ***
> * error: cannot run git init -- have you built things yet?
> make[1]: *** [t0000-basic.sh] Error 1
> make[1]: Leaving directory `/home/Adam Roben/dev/git/t'
> make: *** [test] Error 2

This is a very common configuration on Cygwin, but clearly not a common 
configuration for git developers, or else this error would have been 
corrected already.

Do we want to support having spaces in your path? It doesn't seem hard 
to fix, but it does seem like the kind of problem that will come up over 
and over again if only a very small set of people have this configuration.

-Adam