Test for mod_rewrite even when PHP is run as CGI

[dliessi]

The first commit fixes a bug in current admin/vfront.info.php, where apache_get_modules() is used without checking if it is available. The second commit adds a test for the availability of mod_rewrite that seems to work even if PHP is run as CGI, since it directly tests if mod_rewrite is working. I didn't squash them because you may judge that you are interested only in the first one.

[marciuz]

Hi Davide,

indeed, I world like to merge only the first commit.