HPCC-10279 esdl_srv_engine should return HTTP exceptions

This fixes export issues that had broken the windows build, but
returns to using HTTP Exceptions.

Signed-off-by: Anthony Fishbeck <anthony.fishbeck@lexisnexis.com>
Merge branch 'export_http_exceptions' into candidate-4.2.0

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>