Ignoring [._]*.sw[a-p] instead of *.s[a-w][a-z]

The old pattern was too broad and was making VIM ignore Scheme (*.scm) files.
Now it only matches files that start with . or _.
Merge pull request #765 from martinblech/patch-1

Ignoring [._]*.s[a-w][a-z] instead of *.s[a-w][a-z]