Test a bug ID can be given with a prefix

Enabling possibility to define a prefix for a bug ID, e.g. [[BZ#1234]].
This is needed because some users have been marking bugs with such
format and they often use the same in QA Reports, and also to later
enable linking to multiple Bugzilla servers.
indexOf does not work in IE, surprise surprise
Correctly parse bugs with a prefix, e.g. [[BZ#1234]]

Added handling bug tags with a prefix.