Properly detect boost141 libs/headers on el5.

refs #4772
Update documentation.
Fix group check.

Fixes #4816
Implement global attributes.
Use script variables for global options.
Convert global attributes to script variables.
Add config_lexer.cc, config_parser.cc and config_parser.h to the dist tarball.

Fixes #4814
Update INSTALL file.
Redirect getent/dscl output.
Documentation: Hide internal definition.
Fix boost detection on CentOS 5.x.
spec: Add sub packages icinga2-{doc,common}.

refs #4533
Fix boost detection on CentOS 5.x (again).
spec: Drop boost detection workaround.
Build fix for CentOS 5.9.

Fixes #4819
Fix the example config.
spec: Fix user/group creation, only call i2enfeature ido-mysql on fresh install.

refs #4772
refs #4811
spec: Move ITL into -common.

refs #4811
refs #4772
Documentation: Fix i2enfeature example.
spec: Drop user/group requires.