Revert "Compile StrIntUtilsNoStrictAliasing.cpp with -O2 instead of -O3"

This reverts commit 808e2c2a0fceb12464e1d19c9b85680090c180b3.
Compile StrIntUtilsNoStrictAliasing.cpp with -O2 instead of -O3

Compiling with -O3 causes segfaults on RHEL 6.
Add a server optimization guide
Update server optimization guide

[ci:skip]
Fix documentation scripts when hosting on www.phusionpassenger.com

[ci:skip]
Update optimization guide

[ci:skip]
Cleanup changelog

[ci:skip]
Bump version to 5.0.0.beta1
Do not build Debian packages and do not create Homebrew submission when releasing beta packages
Small changelog update

[ci:skip]
Make `passenger-config system-metrics` work properly if the agent is installed in ~/.passenger.

Closes GH-1304.
Fix handling of multiple Set-Cookie headers.

Closes GH-1296.
Declare some Javascript variables with 'var'.

Closes GH-1297.
Disable user switching in Passenger Standalone
Update changelog.

[ci:skip]
Fix Linux OS name detection

Avoids problems like https://groups.google.com/forum/#!msg/phusion-passenger/IDacgpHxPiQ/iS2essCu_-UJ
Correctly output Set-Cookie headers
Allow HEAD requests to hit the cache
Do not update Homebrew formula for beta releases
When setting REMOTE_ADDR in Apache, use useragent_ip instead of client_ip.

Closes GH-1284.