@go.log_command should set _GO_LOG_FORMATTING

[mbland]

I noticed when running ./go install from mbland/dev-setup that the scripts that call @go.log inside a @go.log_command call weren't colorizing their output. Should be an easy fix for @go.log_command to set _GO_LOG_FORMATTING='true' when the output file descriptor is a terminal.

Now that I think about it, _GO_LOG_FORMATTING could be an array, so that it could be set for each file descriptor as appropriate...