For example, when trying to gift gold to /u/live_wire_ (who is actually a random reddit user), after you choose the amount of gold to gift, enter the details, and click "give", it'll take you to a confirm screen that says:
"You're about to give 1 month of gold to..."
But instead of displaying "live_wire_" on this page, it'll display the username as "livewire".
It's worth noting that the url still displays the proper username, and your gift will still go to /u/live_wire_. However, the "confirm" message does not display the underscores.
Replace _ in username to avoid markdown issues
When gifting a user gold, it displays their username using markdown,
so any underscores need to be replaced first to avoid having part of
a username between them interpreted as italics.
Fixes issue #714