Rename env var BROWSER to DRIVER to fix Launchy

In testing found an incompatibility with setting an environment variable called BROWSER and trying to use Launchy. It seems this is a variable used by the OS for setting what the default browser is, and in turn Launchy references it when trying to open the saved page.

So this change updates the ENV VAR and corresponding code and comments to use DRIVER instead of BROWSER.

features/support/env.rb

@@ -9,9 +9,14 @@
 # or (to have a pause of 1 second between each step):
 # PAUSE=1 bundle exec cucumber
 # To use chrome instead of Firefox
-# BROWSER=chrome bundle exec cucumber
+# DRIVER=chrome bundle exec cucumber
 # Else the default will use the poltergiest headless browser
 # bundle exec cucumber
+#
+# N.B. Initially the env var was named BROWSER but it was found this was
+# a key environment variable for Launchy and changing it broke Launchy.
+# Therefore have settled in DRIVER as a replacement, though its not as
+# clear to quke's intended audience.
 
 # Capybara defaults to CSS3 selectors rather than XPath.
 # If you'd prefer to use XPath, just uncomment this line and adjust any
@@ -53,19 +58,19 @@
 end
 
 # The choice of which browser to use for the tests is dependent on what the
-# environment variable BROWSER is set to. If not set we default to using
+# environment variable DRIVER is set to. If not set we default to using
 # poltergeist
-browser = case (ENV['BROWSER'] || '').downcase.strip
-          when 'firefox'
-            :firefox
-          when 'chrome'
-            :chrome
-          else
-            :poltergeist
-          end
+driver = case (ENV['DRIVER'] || '').downcase.strip
+         when 'firefox'
+           :firefox
+         when 'chrome'
+           :chrome
+         else
+           :poltergeist
+         end
 
-Capybara.default_driver = browser
-Capybara.javascript_driver = browser
+Capybara.default_driver = driver
+Capybara.javascript_driver = driver
 
 # We use cucumber's AfterStep hook to insert our pause between pages if
 # one was set