Allow SSH agent installed and managed by posh-git to also be usable from other non-PowerShell processes (e.g. Tower Git client for Windows).

profile.ps1

# Add this into your profile AFTER posh-git has been loaded and the SSH agent
# has been started.

[void][Environment]::SetEnvironmentVariable("SSH_AGENT_PID", [Environment]::GetEnvironmentVariable("SSH_AGENT_PID"), [EnvironmentVariableTarget]::User)
[void][Environment]::SetEnvironmentVariable("SSH_AUTH_SOCK", [Environment]::GetEnvironmentVariable("SSH_AUTH_SOCK"), [EnvironmentVariableTarget]::User)

# It may make it a little slower (as apparently writing to the user environment
# is slow), but will mean the SSH agent is visible to other processes.