Add '--force' to 'new' command. Implements #1104
Merge latest commits from mojombo/jekyll
Merge in additional changes from mojombo/jekyll
Extract check for force to improve readability
Add ? to preserve_source_location
Fix for issue #1122.
Merge pull request #1115 from clang1234/master

Add --force flag to new command
Update history to reflect merge of #1115
Merge pull request #1123 from mainerror/docs_overflow_auto

Documentation highlight boxes shouldn't show scrollbars if not necessary. Fixes #1122.
Update history to reflect merge of #1123