Add GOROOT/bin to tool lookup path
Add GOROOT/bin to tool lookup path

Add GOROOT/bin to tool lookup path. The arch-specific GOROOT bin path
isn't necessarily used everywhere (e.g. brew/OSX).

Improve the error message when a tool can't be found.

Mistobaan/GoTools,stevekuznetsov/GoTools,bparees/GoTools,stevekuznetsov/GoTools,ironcladlou/GoTools,nuance/GoTools,liuhewei/gotools-sublime,Mistobaan/GoTools,nuance/GoTools,ironcladlou/GoTools,liggitt/GoTools,liggitt/GoTools,bparees/GoTools