require "pio" explicitly.
Version bump.
Merge branch 'release/0.4.2' into develop
fix rspec backtrace on launch

Not sure if this is the right way to fix it, but without this change
rspec failed to execute (with or without arguments):

/usr/share/rubygems/rubygems/core_ext/kernel_require.rb:51:in `require': cannot load such file -- pio (LoadError)
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:51:in `require'
	from /tmp/trema/spec/spec_helper.rb:27:in `<top (required)>'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:51:in `require'
	from /usr/share/rubygems/rubygems/core_ext/kernel_require.rb:51:in `require'
	from /tmp/trema/spec/trema/app_spec.rb:19:in `<top (required)>'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/configuration.rb:896:in `load'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/configuration.rb:896:in `block in load_spec_files'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/configuration.rb:896:in `each'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/configuration.rb:896:in `load_spec_files'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/command_line.rb:22:in `run'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/runner.rb:80:in `run'
	from /usr/local/share/gems/gems/rspec-core-2.14.5/lib/rspec/core/runner.rb:17:in `block in autorun'
fix loss of some OFPT_PORT_MOD messages

The ofp_port_mod.advertise field is a bitmask of OFPPF_* constants and
its validation must be based on the PORT_FEATURES constant (as it is in
the validate_phy_port() function). But the validate_port_mod() function
used PORT_CONFIG constant instead and erroneously failed the check for
a correct message with any of the following bits set:
* OFPPF_COPPER
* OFPPF_FIBER
* OFPPF_AUTONEG
* OFPPF_PAUSE
* OFPPF_PAUSE_SYM

The controller would log an error with code ERROR_INVALID_PORT_FEATURES
(-49) and discard the message. This change fixes the bug.
list recent Fedora releases in README