Use Ruby 2.x compatible rescue clauses

Ruby 2.x doesn't support non-class/module arguments to rescue clauses.
Ruby 1.9 only supported it due to what is now considered a regression:

https://bugs.ruby-lang.org/issues/4438

Remove string arguments from rescue clauses to prevent TypeErrors from
being raised during rescue attempts.
Merge pull request #1296 from ironcladlou/ruby2-exception-handling

Use Ruby 2.x compatible rescue clauses
Fix build on rbx (it failed previously)
Merge pull request #1306 from abotalov/fix_rbx_build

Fix build on rbx (it failed consistently previously)
optimization of Capybara::RackTest::Node#unnormalized_text
Merge pull request #1309 from twalpole/visible_optimization

Optimization of Capybara::RackTest::Node#unnormalized_text while checking visibility
New API for working with windows (switching/finding/closing/opening/etc.)
Bugfixing for windows API (primarily switch_to_window and within_window)
Add maximize window
Resize/get size/close should work for non-current window