simplemerge: let filemerge check for binary inputs
This is similar to the previous patch, but here we put a specialized
copy of `simplemerge._verifytext()` in the the `filemerge` module
instead.
Differential Revision: https://phab.mercurial-scm.org/D12147
$ cat >> $HGRCPATH << EOF
> [extensions]
> fastannotate=
> EOF
$ hg init repo
$ cd repo
changes to whitespaces
$ cat >> a << EOF
> 1
>
>
> 2
> EOF
$ hg commit -qAm '1'
$ cat > a << EOF
> 1
>
> 2
>
>
> 3
> EOF
$ hg commit -m 2
$ hg fastannotate -wB a
0: 1
0:
1: 2
0:
1:
1: 3