Information providers for A-REX.

Currenly all information collection for A-REX is done by these scripts.
Collected data is presented in 2 formats (classic NG schema and GLUE2 schema)
rendered in XML.

CEinfo.pl      - driver for information collection. It calls all other infomation
                 collectors and prints results in XML.

InfoChecker.pm  - used to validate options and results against a simple
                 'schema' (not XML Schema)
GMJobsInfo.pm - collects information about jobs from grid manager status files
HostInfo.pm - collects other information that can be collected on the front end
	      (hostname, software version, disk space for users, installed
              certificates, Runtime environments ...)
LRMSInfo.pm - collects information that is LRMS specific (queues, jobs, local
              user limits ...)
XXXXmod.pm  - plugins for LRMSInfo implementing the new LRMS module interface,
              such as:
    FORKmod.pm - Fork information module
    SGEmod.pm  - SGE information module
    SLURMmod.pm  - SLURM information module
    ARC0mod.pm - special module that loads ARC0 information modules and does
                 the conversion between the old interface and the new one.
                 NOTE: New development should NOT develop against this 
                       implementations. These are obsolete and deprecated.
PBS.pm, LL.pm, LSF.pm, Condor.pm, SLURM.pm - ARC0 information modules
                 NOTE: New development should NOT develop against this 
                       implementations. These are obsolete and deprecated.

ARC0ClusterInfo.pm - combines all information about A-REX and produces
                     information structured according to the classic NG schema.
ARC1ClusterInfo.pm - combines all information about A-REX and produces
                     information structured according to the GLUE2 schema.

Extended information:

CEinfo.pl uses *Info.pm to read all information. LRMSInfo in turn uses 
${LRMS}mod.pm and ${LRMS}.pm to get information.

That information is aggregated by CEinfo.pl. CEinfo.pl then gives that data to 
ARC*ClusterInfo.pm which transforms the output to the appropriate format.
Lastly, CEinfo.pl uses *Printer.pm to generate ldif/xml. 

Loading structure:
CEinfo.pl loads: ARC*ClusterInfo.pm, GLUE2*Printer.pm, NGldifPrinter.pm, 
                 {Host,RTE,GMJobsInfo,LRMS}Info.pm, InfosysHelper.pm,
LRMSInfo loads: ${LRMS}mod.pm, ARC0mod.pm
ARC0mod.pm: loads ${LRMS}.pm 

# TODO: update description of the call chain when ARC 6.0 config is in place.
Call-chain:

To be described
