subrepo: better error messages in _ensuregit...
subrepo: better error messages in _ensuregit
This patch improves the error messages raised when an OSError occurs, since
simply re-raising the exception can be both confusing and misleading. For
example, if "hg identify" is run inside a repository that contains a Git
subrepository and the git binary could not be found, it'll exit with the message
"abort: No such file or directory". That implies "identify" has a problem
reading the repository itself. There's no way for the user to know what the
real problem is unless they dive into the Mercurial source, which is what I
ended up doing after spending hours debugging errors while provisioning a VM
with Ansible (turns out I forgot to install Git on it).
Descriptive errors are especially important on Windows, since it's common for
Windows users to forget to set the "Path" system variable after installing Git.
