tests/test-empty-file.t

convert: update source shamap when using filemap, just as when not using filemap

The reverse mapping was introduced in 2147a734dcf9 to make roundtrip
conversions possible ... but it did not work when using filemap.

Roundtrips with filemaps will of course only work flawlessly if inverse
mappings are used.

Especially, if a lossy convert mapping is used in one direction, then only
linear lines of development can be converted in the other direction. With this
constraint convert will do the right thing by assuming that excluded files
haven't been changed.)

A test case with general coverage of hg-hg roundtrips with filemap is added.

(There a cases where adding records of converted revisions to the shamap in the
source repository doesn't work - especially when converting the same repo to
several other repos and back. It would arguably be better if convert only
updated the shamaps in the target repo but read shamaps from both the source
and and target repo ... but that is a different story. Making the stuff we have
work consistently is step forward no matter what.)

  $ hg init a
  $ cd a
  $ touch empty1
  $ hg add empty1
  $ hg commit -m 'add empty1'

  $ touch empty2
  $ hg add empty2
  $ hg commit -m 'add empty2'

  $ hg up -C 0
  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
  $ touch empty3
  $ hg add empty3
  $ hg commit -m 'add empty3'
  created new head

  $ hg heads
  changeset:   2:a1cb177e0d44
  tag:         tip
  parent:      0:1e1d9c4e5b64
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add empty3
  
  changeset:   1:097d2b0e17f6
  user:        test
  date:        Thu Jan 01 00:00:00 1970 +0000
  summary:     add empty2
  

  $ hg merge 1
  1 files updated, 0 files merged, 0 files removed, 0 files unresolved
  (branch merge, don't forget to commit)

Before changeset 05257fd28591, we didn't notice the
empty file that came from rev 1:

  $ hg status
  M empty2
  $ hg commit -m merge
  $ hg manifest --debug tip
  b80de5d138758541c5f05265ad144ab9fa86d1db 644   empty1
  b80de5d138758541c5f05265ad144ab9fa86d1db 644   empty2
  b80de5d138758541c5f05265ad144ab9fa86d1db 644   empty3

  $ cd ..