(DOC-1111) Port over interim changes to 3.6 docs, up thru 6475371
DOC-1119: update cipher settings in Passenger guide
DOC-1124 Added deprecated words to lang_reserved.

Added keywords to lang_reserved; words are deprecated in 3.7 and reserved in 4.0.
Edit to reflect deprecation of vars with initial caps

Edited lang_reserved and lang-_variables to reflect 3.7 deprecation of vars beginning with uppercase letters.
Edit to reflect relative namespacing fix in 4.0 and future parser

Added several notes saying that relative namespacing is gone in 4.0 and in the future parser as of 3.7. Linked to future parser page in some, but not all, of these notes.