Fixes and updates for serendipity_event_spamblock by DLange (2.0 branch)

[PATCH 1/4] remove serendipity_serverOffsetHour() workaround as this
 function is now in core

[PATCH 2/4] remove blogg.de anti-spamlist support as it has been
 discontinued

[PATCH 3/4] proper locking of .htaccess file to prevent race
 condition and partial file over-writes

[PATCH 4/4] allow multiple Deny From lines in .htaccess so more IPs
 can be simultaneously  blocked for busy sites