Better autodetection of Soft Tabs.

Check for the presence of a space, instead of the absence of a tab.
This ensures that Soft Tabs will not be activated on a file that (for
example) starts with a BOM or something, but is otherwise full of hard
tabs.
merge latest upstream master
updated regex in usesSoftTabs to only look for Tab and Space
Merge pull request #3369 from khakionion/master

Better autodetection of Soft Tabs.