Template installation fails when OS tmpdir is on different filesystem/disk

[jay7x]

Template installation code uses rename() call internally, that fails when source and destination paths are not on the same filesystem.
There are few options how to solve it:

1. Use temporary directory under template directory path (and mention that in the documentation explicitly), so rename() never fails.
2. Just mention that explicitly in the documentation and do nothing.
3. Implement fallback to copy & unlink if rename() fails.