Subrepository support

[PioneerAxon]

Subrepositories [0] are not supported.

This will be easy to set up using git submodules (Just recursively clone each hg:: from .hgsub file using "git submodule add").

[0] : http://mercurial.selenic.com/wiki/Subrepository

[glandium]

It's not as trivial as it seems:

• git submodules use "git links" to store the equivalent of .hgsubstate, which means the submodules need to be cloned before the main repo to know their git sha1s. This kind of breaks how git submodules work. At least, this requires some additional integration effort.
• mercurial subrepos can be used for non-mercurial repos
• The .hgsub and .hgsubstate file must be left out of the git clone and regenerated from the state of git submodules. This likely will require to store additional state in the git2hg notes, because .hgsub files are not necessarily ordered aiui.

It's not a priority for me, at this point, to implement this.