test PubChem access

Test model loading from PubChem; JSmol 14.6.4_2016.10.26

Lightweight JSmol	HTML5 JSmol

works in both; retrieves https://pubchem.ncbi.nlm.nih.gov/rest/pug/compound/cid/173183/SDF?record_type=3d

fails in Lightweight; retrieves https://pubchem.ncbi.nlm.nih.gov/rest/pug/compound/name/57-87-4/SDF?record_type=3d

works