cmd/go: show position in error for wrong signature in test functions
cmd/go: show position in error for wrong signature in test functions

Change-Id: Ie915dc2fc32a31d31f566ac931ccecb506559645
Reviewed-on: https://go-review.googlesource.com/19888
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

4ad/go,miolini/go,miolini/go,4ad/go,binarycrusader/go,akutz/go,miolini/go,theif519/go,akutz/go,ganboing/go-esx,Samurais/go,Samurais/go,golang/go,ImJasonH/go,vanloswang/go,nawawi/go,Cofyc/go,codestation/go,goodlang/good,CAFxX/go,akutz/go,ganboing/go-esx,Samurais/go,derekmarcotte/go,Samurais/go,ganboing/go-esx,akutz/go,binarycrusader/go,Cofyc/go,Cofyc/go,momchil-velikov/go,nawawi/go,josharian/go,binarycrusader/go,nawawi/go,suncycheng/go,derekmarcotte/go,linux-on-ibm-z/go,derekmarcotte/go,akutz/go,ganboing/go-esx,derekmarcotte/go,golang/go,theif519/go,cloudflare/go,miolini/go,derekmarcotte/go,momchil-velikov/go,polyverse-security/go,mwhudson/go,josharian/go,theif519/go,vsekhar/elastic-go,ImJasonH/go,codestation/go,theif519/go,golang/go,4ad/go,4ad/go,vanloswang/go,linux-on-ibm-z/go,codestation/go,miolini/go,derekmarcotte/go,momchil-velikov/go,CAFxX/go,linux-on-ibm-z/go,golang/go,theif519/go,4ad/go,polyverse-security/go,linux-on-ibm-z/go,nawawi/go,ImJasonH/go,4ad/go,ganboing/go-esx,nawawi/go,vsekhar/elastic-go,nawawi/go,linux-on-ibm-z/go,codestation/go,linux-on-ibm-z/go,goodlang/good,vanloswang/go,mwhudson/go,theif519/go,vsekhar/elastic-go,derekmarcotte/go,vsekhar/elastic-go,polyverse-security/go,mwhudson/go,vsekhar/elastic-go,miolini/go,CAFxX/go,ImJasonH/go,christopher-henderson/Go,suncycheng/go,josharian/go,binarycrusader/go,Cofyc/go,mwhudson/go,momchil-velikov/go,golang/go,suncycheng/go,cloudflare/go,polyverse-security/go,CAFxX/go,Cofyc/go,Samurais/go,ganboing/go-esx,codestation/go,vanloswang/go,theif519/go,nawawi/go,vanloswang/go,ImJasonH/go,suncycheng/go,ImJasonH/go,goodlang/good,vsekhar/elastic-go,Samurais/go,goodlang/good,ImJasonH/go,josharian/go,vsekhar/elastic-go,goodlang/good,binarycrusader/go,akutz/go,mwhudson/go,codestation/go,goodlang/good,golang/go,4ad/go,mwhudson/go,josharian/go,golang/go,goodlang/good,akutz/go,vsekhar/elastic-go,cloudflare/go,binarycrusader/go,4ad/go,codestation/go,linux-on-ibm-z/go,vanloswang/go,miolini/go,Samurais/go,CAFxX/go,josharian/go,miolini/go,binarycrusader/go,cloudflare/go,momchil-velikov/go,CAFxX/go,codestation/go,Cofyc/go,CAFxX/go,momchil-velikov/go,cloudflare/go,linux-on-ibm-z/go,Cofyc/go,suncycheng/go,polyverse-security/go,ganboing/go-esx,Cofyc/go,suncycheng/go,cloudflare/go,vanloswang/go,josharian/go,cloudflare/go,theif519/go,binarycrusader/go,ImJasonH/go,mwhudson/go,goodlang/good,suncycheng/go,derekmarcotte/go,cloudflare/go,polyverse-security/go,momchil-velikov/go,Samurais/go,suncycheng/go,polyverse-security/go,mwhudson/go,akutz/go,golang/go,momchil-velikov/go,vanloswang/go,CAFxX/go,josharian/go,polyverse-security/go,ganboing/go-esx,nawawi/go