generalized index files, changed STRIP_INDEX_HTML to STRIP_INDEXES
added warning when variable changes
Avoid crashing if user does a deploy with no commands
Merge branch 'master' of github.com:ralsina/nikola
updated changelog
Fix #468
Merge pull request #467 from jbarratt/configurable_index_file

generalized index files, changed STRIP_INDEX_HTML to STRIP_INDEXES