Fix Linux OS name detection

Avoids problems like https://groups.google.com/forum/#!msg/phusion-passenger/IDacgpHxPiQ/iS2essCu_-UJ
Fix a NULL bug in HeaderTable::erase()
Credit Igor Vuk.
Support Ruby 2.2 rb_thread_call_without_gvl()

Closes GH-1314.
Support Ruby 2.2 rb_thread_call_without_gvl()

Closes GH-1314.
Bump version to 4.0.55, update changelog
Merge branch 'stable-4.0'

Conflicts:
	CHANGELOG
	ext/common/Constants.h
	lib/phusion_passenger.rb
Fix File descriptor leak related to GH-1324.
Merge pull request #1325 from popox/fix-gh-1324

Fix File descriptor leak related to GH-1324.
Fix File descriptor leak related to GH-1324.
Bump version to 4.0.56, update changelog and contributors list
Merge branch 'stable-4.0'

Conflicts:
	CHANGELOG
	ext/common/Constants.h
	lib/phusion_passenger.rb
Fix passenger start --thread-count
Fix 'passenger-config admin-command' parameter parsing
Improved Node.js request load balancing

Closes GH-1322. Thanks to Charles Vallières for the analysis.
Improved Node.js request load balancing
Merge branch 'stable-4.0'

Conflicts:
	ext/common/ApplicationPool2/Process.h
Apache: fix support for gzipped chunked responses

Closes GH-1309.
Bump version to 5.0.0.beta2
Fix a WebSocket-related crash