Auto merge of #2315 - alexcrichton:decode-some-signals, r=brson
Auto merge of #2315 - alexcrichton:decode-some-signals, r=brson

Instead of text that looks like

    Process failed (signal: 11)

the text now looks like:

    Process failed (signal: 11, SIGSEGV: invalid memory reference)

Closes #2315

sbeckeriv/cargo,blaenk/cargo,rust-lang/cargo,mark-buer/cargo,tshepang/cargo,blaenk/cargo,achanda/cargo,achanda/cargo,tshepang/cargo,blaenk/cargo,brson/cargo,ThinTim/cargo,mark-buer/cargo,rust-lang/cargo,achanda/cargo,rustyhorde/cargo,AndiDog/cargo,mark-buer/cargo,brson/cargo,tshepang/cargo,brson/cargo,eminence/cargo,vojtechkral/cargo,vojtechkral/cargo,durka/cargo,durka/cargo,sbeckeriv/cargo,nipunn1313/cargo,nipunn1313/cargo,tshepang/cargo,ThinTim/cargo,AndiDog/cargo,sbeckeriv/cargo,blaenk/cargo,rustyhorde/cargo,ThinTim/cargo,eminence/cargo,rust-lang/cargo,tsurai/cargo,achanda/cargo,AndiDog/cargo,tsurai/cargo,durka/cargo,eminence/cargo,blaenk/cargo,eminence/cargo,vojtechkral/cargo,rustyhorde/cargo,ThinTim/cargo,tsurai/cargo,AndiDog/cargo,brson/cargo,tsurai/cargo,mark-buer/cargo,AndiDog/cargo,sbeckeriv/cargo,nipunn1313/cargo,nipunn1313/cargo,rustyhorde/cargo,durka/cargo,brson/cargo,rust-lang/cargo,vojtechkral/cargo,mark-buer/cargo,tsurai/cargo,ThinTim/cargo