[Patch] fix small memleak in _dbus_setenv()

[Havoc Pennington]

Hi,

You can't fix this leak; putenv doesn't copy the string. There should
be a comment in the code about this, if not, a good patch would be to
add one.

This is just a bug in the putenv() API design, which is why setenv and
unsetenv are preferred.

Havoc