Support hg submodules (.hgsub)

[christophelevis]

Having submodules in the repository produce following failure:

10:05:18.466 DEBUG - Executing: hg blame -w -v --user --date --changeset hotspot/src/share/vm/utilities/globalDefinitions_xlc.hpp
10:05:18.469 DEBUG - The mercurial blame command [hg blame -w -v --user --date --changeset hotspot/src/share/vm/utilities/exceptions.cpp] failed: abort: path 'hotspot/src/share/vm/utilities/exceptions.cpp' is inside nested repo 'hotspot'

[simonbrandhof]

Ticket moved to https://jira.sonarsource.com/browse/SONARHG-6