'undefined' being written to tsd.d.ts

[rcollette]

I believe this may be happening when a run gulp and I have forgotten to use resolve when adding a definition. For example. I add gulp-util using:
tsd install gulp-util -s
I then run a task in gulp and get the error message
ProjectPath/typings/gulp-util/gulp-util.d.ts(7,1): 6053 File 'ProjectPath/typings/vinyl/vinyl.d.ts' not found.
After that the word undefined appears in tsd.d.ts which results in the error
ProjectPath/typings/tsd.d.ts(6,1): 1036 Statements are not allowed in ambient contexts.

[aciccarello]

For anyone else who runs into this issue. I had this happen briefly when I was running tsd while I had left a gulp + browserify + watchify + tsify build running in another window. Once I stopped my build and re-ran tsd, the file was fine.