Extended command 'record' so that XML representation of original record

Extended command 'record' so that XML representation of original record
can be returned. Bug #1172. If parameter 'offset' is given for command
'record' the original record is returned and offset is the record offset
within cluster (merged) record, where 0=first, 1=second, etc.. If no record
at offset is given diagnostic RECORD_FAIL is returned.  When offset
is given, the value of parameter 'syntax' and 'esn' specifies the
record syntax and element set respectively. If any of these are omitted
the present request also omits them. The code to convert from 'raw' to
XML is combined into one function record_to_xml. Note that OPAC records
are not converted to XML yet.