[SCM-530] Add support for git submodules to git SCM provider

**[Chas Emerick](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cemerick)** opened **[SCM-530](https://issues.apache.org/jira/browse/SCM-530?redirect=false)** and commented

Pretty self-explanatory. Example fallout of this issue: release:perform on a project that refers to other git repos as submodules cannot succeed.

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**Affects:** 1.3

**Issue Links:**
- [SCM-844](https://issues.apache.org/jira/browse/SCM-844) Add support for git submodules to jgit SCM provider

**Remote Links:**
- [GitHub Pull Request #179
](https://github.com/apache/maven-scm/pull/179)

7 votes, 12 watchers

Start with the Git SCM provider and review remote pull request #179, along with JIRA SCM-530 and related SCM-844. Verify how release:perform behaves for projects containing Git submodules; done means the Git provider supports those projects successfully.

Written by the indexing model from the issue text.