Better guide users when no source-maps exist.

[lramos15]

I previously setup a very basic Typescript project and forgot to enable source maps. The default debug configuration kept trying to run my Typescript files without giving explanation why. I did not receive the breakpoints won't bind warning because the debugger would immediately stop and start since the Typescript files were syntactically incorrect when interpreted as Javascript. I've included a simple sample project zipped below example-debug.zip