match_when_negated does not handle expectation failures like match does

[myronmarston]

The definition of match in the matcher DSL rescues ExpectationNotMetError and returns false, allowing expectations to be used in match blocks:

rspec-expectations/lib/rspec/matchers/dsl.rb

Lines 64 to 65 in 6717b72

	rescue RSpec::Expectations::ExpectationNotMetError
	false

However, match_when_negated does not do this:

rspec-expectations/lib/rspec/matchers/dsl.rb

Lines 76 to 81 in 6717b72

	def match_when_negated(&match_block)
	define_user_override(:does_not_match?, match_block) do |actual|
	@actual = actual
	super(*actual_arg_for(match_block))
	end
	end

This should be fixed, as these two methods should have parity with respect to how expectation failures are treated.

Note that I'm currently working on some edits in this area as part of #776 so whoever works on this may want to hold off until that PR is merged to reduce the likliehood of merge conflicts.