Fix blacklisting of URLs to download

Fixes a reported crash and prevents multiple downloads of the
same file in case the URL is escaped in different ways.

Reported-by: Frédéric <vfrederix@gmail.com>
Perl test suite: Substitue server port in HTTP headers
Add space after function names
GnuTLS support for --secure-protocol=TLSv1_1|TLSv1_2

The code seemed to be forgotten.
Also added a message before aborting Wget in such a case.
Select most secure challenge from WWW-Authenticate

This patch also adds support for multiple challenges per
WWW-Authenticate header line.
The test Test-auth-both.py now succeeds and thus is taken away
from XFAIL_TESTS (expected to fail tests).
Replace all occurences of free() with xfree()