[feature request] Find files based on the current buffer name

The [nixprime/cpsm](https://github.com/nixprime/cpsm) CtrlP matcher for CtrlP has this awesome feature:
> cpsm will still attempt to perform matching on an empty query based on the open file in the current buffer.

When Ctrlp is first open, a first match is performed based on the current buffer name.

I like this feature a lot because it allows me to quickly switch between the implementation file and his test file.
eg:
Having the file `foo.go` buf active, press ``, the first match of the list would be `foo_test.go` press enter, your done!

The current buffer name has to be ignore from the search result. (Which is another nice feature by itself!)

I know that swapping between file of similar name can be done in `vim-projectionist`, but I tend to prefer having one very smart way to select file rather than many.