This is less magical than rephrasing ships-with-hg-core as internal, and
we can distinguish "internal" liar. "tested with: internal" will be hidden
by the next patch.
Add debugextensions command to help users debug their extension
problems. If there are no extensions command prints nothing,
otherwise it prints names of extension modules. If quiet or
verbose option is not specified it prints(after extensions name)
last version of mercurial in which given module was tested for
non internal modules or not tested with user mercurial version.
If verbose is specified it prints following information for every
extension: extension name, import source, testedwith and buglink
information.
Extensions are printed sorted by extension name.
