tests/test-issue1438.t

rust-re2: add wrapper for calling Re2 from Rust

This assumes that Re2 is installed following Google's guide. I am not sure
how we want to integrate it in the project, but I think a follow-up patch would
be more appropriate for such work.
As it stands, *not* having Re2 installed results in a compilation error, which
is a problem as it breaks install compatibility. Hence, this is gated behind
a non-default `with-re2` compilation feature.

Differential Revision: https://phab.mercurial-scm.org/D7910

#require symlink

https://bz.mercurial-scm.org/1438

  $ hg init

  $ ln -s foo link
  $ hg add link
  $ hg ci -mbad link
  $ hg rm link
  $ hg ci -mok
  $ hg diff -g -r 0:1 > bad.patch

  $ hg up 0
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  $ hg import --no-commit bad.patch
  applying bad.patch

  $ hg status
  R link
  ? bad.patch