SUB-MAPPINGS: This type of mapping allows to use an ordinary Perl
subroutine to map a classification string into a new string. The
subroutine used is defined in a config file.

Use of SUB-MAPPINGS: Add the usual specification of virtual
classifications in acc_types. Store the mapping file in the usual
directory (/var/opt/openit/etc/mappings). The format of the mapping
file is as follows:

[SUB-MAPPINGS]:
sub {
    my( $value ) = @_;
    # Some Perl code...
    return ...;
}

For instance, a mapping file to split the classification on backslash
and use the last field could look like this:

[SUB-MAPPINGS]:
sub {
    my( $value ) = @_;
    my $sep = '\\\\'
    my @fields = split( $sep, $value );
    return pop @fields;
}

(Perl's split is using a regexp, and therefore the backslashes have to
be escaped this way.)

NOTE: If the new virtual classification is added in the
classvar_mapping_config, then a call to generate_classvar_mapping wil

This patch fixes ability to report with top and threshold settings
with ABSAVG values, which did not work after patch #434.

In addition, the backend supports a directive in openit.cfg for
setting precision of values in html reports, like:

REPORTS_DECIMAL_DIGITS 3

will set use of three digits in fractional part of values in html
reports. A "+" or a "-" can be added to force rounding up or down.