issue102: fix - index caches against domain name

Fixes problems with certificates where RDNs types not always printable:
$ openssl x509 -in BrGrid.pem -noout  -subject -nameopt multiline,show_type
subject= 
    countryName               = PRINTABLESTRING:BR
    organizationName          = UTF8STRING:ICPEDU
    organizationName          = UTF8STRING:UFF BrGrid CA
    commonName                = UTF8STRING:UFF Brazilian Grid Certification Authority

(cherry picked from commit e70c71dc28597085618e6696ddbdfbf9fd290a7a)
(cherry picked from commit 84a05be6d6acba1ec4fa341db7412a1db12832c6)
(cherry picked from commit 144e9bc227cca16e2b097423b6deba77ba917eeb)
Signed-off-by: Tigran Mkrtchyan <tigran.mkrtchyan@desy.de>