convert: add convert.git.skipsubmodules option This adds an option to not pull in gitsubmodules during a convert. This is useful when converting large git repositories where gitsubmodules were allowed historically, but are no longer wanted.

paths: move path validation logic to its own function Hard coding the '.hg' path in the paths class made it difficult for the hggit extension to pull from gitrepos. This patch moves the logic out to it's own function so extensions can add additional checks to what is a valid path (i.e. a git repo is valid when hggit is enabled).