Search.pm minor cleanup

Search.pm minor cleanup

Trying to move towards enabling warnings.
Add warn for unknown $query_type.
Use common $dbh.

push @array, ({key1=>value1...}); is the same as
push @array, {key1=>value1...};

if ( scalar(@$arrayref) > 0 ) is the same as
if (scalar @$arrayref)

Lines like:
    my @operators = @$operators if $operators;
are bad because we need @operators to be declared and in scope later,
even if it is undef.  Without $operators, the variable is not in scope.

Signed-off-by: Galen Charlton <galen.charlton@liblime.com>
Signed-off-by: Henri-Damien LAURENT <henridamien.laurent@biblibre.com>