remove pre-release from 8.0.6-branch
edits to 8.0.6 version history item and new knob definition for
DAGMAN_USE_OLD_DAG_READER  #4171
Merge branch 'V8_0_6-branch' into V8_0-branch
have V8_0-branch of the manual be for 8.0.7
Merge branch 'V8_0-branch'

Conflicts:
	doc/condor-macros.tex