Implement config editing for mercurial

Issue #511

Signed-off-by: Michal Čihař <michal@cihar.com>
Test unicode names and fix them for Mercurial

Signed-off-by: Michal Čihař <michal@cihar.com>
Implement generic get_object_hash

This is for VCS who don't store object hash as Git.

Issue #511

Signed-off-by: Michal Čihař <michal@cihar.com>
Improve error handling in VCS module
Remove debug code

Signed-off-by: Michal Čihař <michal@cihar.com>
Correctly handle empty values in Mercurial settings

Signed-off-by: Michal Čihař <michal@cihar.com>
Implement tests for Mercurial configure_remote

Issue #511

Signed-off-by: Michal Čihař <michal@cihar.com>