mxcl/homebrew#19430

http://developer.github.com/changes/2013-01-31-user-agent-will-soon-be-mandatory/

fixes #229

Fixes #299, closes #300

Fixes #288

Fixes #280

Otherwise web pages will be actually opened if the default browser
command is not `open`. Browse tests will all fail as the command will
show up in history only when the fakebin `open` acts as the browser.

Fixes #274

Fixes #232, references #270

Thanks Yahor Radtsevich

References #232, #40, #236

references #269, #189

Fixes #263

Fixes #254

Fixes #252