Change name of transpiled file if it matches the name of the output file to allow source maps to work #4301

see systemjs/systemjs#636 (comment) for more details

from Guy Bedford (@guybedford) comments:

To see the in-browser transpilation, open for example https://github.com/systemjs/systemjs/blob/master/test/test-typescript.html, and see that the original ES6 is not present in comparison to others. Looking at the original source it seems like the reason is that the source map looks like:

{"version":3,"file":"es6-circular1.js","sourceRoot":"","sources":["es6-circular1.js"],"names":["p"],"mappings":";;QACW,CAAC,EACD,CAAC;IACZ;QACEA,EAAEA,CAACA,CAACA,CAACA,CAACA;YACJA,eAAAA,CAACA,GAAGA,oBAACA,CAAAA,CAACA;QACRA,IAAIA;YACFA,eAAAA,CAACA,GAAGA,oBAACA,CAAAA,CAACA;IACVA,CAACA;IALD,iBAKC,CAAA;;;;;;;YACD,CAAC,EAAE,CAAC"}

Where the sources and file name are the same. The point is that for in-browser transpilation we have to change the name of the transpiled source to source.js!transpiled so it can have a separate representation in the debugger, but the load.address argument provided to transpile at https://github.com/ModuleLoader/es6-module-loader/blob/master/src/transpiler.js#L78 becomes both the sources and file value.