IDE-246 Add warning to getECLPluginDefinition

Warn plugin developers that the getECLPluginDefinition call has restrictive
calling rules.

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
Merge pull request #4149 from GordonSmith/IDE-246

IDE-246 Add warning to getECLPluginDefinition

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>