Let #breadcrumbs_trail always find closest parent

[denisdefreyne]

Fixes #1278.

#breadcrumbs_trail already supported cases like these:

/index.md
/foo.md.erb
/foo/stuff.html

# trail = [/index.md, /foo.md.erb, /foo/stuff.html]

but now it will also support

/index.md
/1.2.erb
/1.2/stuff.html

# trail = [/index.md, /1.2.erb, /1.2/stuff.html]

[iay]

The fancy functional programming stuff is beyond my 2006-vintage understanding of Ruby but the intent seems right. I will try and do a quick test of this tomorrow and let you know whether it works for my case.

[iay]

Dropping the modified breadcrumbs.rb into my lib/ directory seems to fix my particular use case.