Allow use of query parser prefixes map

[olly]

Implement $addprefix{author,A} or something equivalent. If done as an omegascript command, need to rejig omega.cc and query.cc so that it gets processed before CGI parameter handling happens - this may have other benefits.

[olly]

Now implemented in CVS - the syntax is:

$setmap{prefix,QUERYPREFIX,TERMPREFIX,...}

e.g.:

$setmap{prefix,author,A,subject,XT,abstract,XA}

[olly]

Fixed in 0.7.5