[SCM-1014] Enable scm changelog on files for svnexe provider

**[Clemens Quoß](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=cquoss)** opened **[SCM-1014](https://issues.apache.org/jira/browse/SCM-1014?redirect=false)** and commented

When using the maven scm changelog command in our custom maven release manager phases (used solely for svnexe provider) to check the most recent commit comment of a specific file we face the issue that we first have to do an scm info on the file and then do a scm changelog on the file's directory using the revision retrieved.

This is necessary because the implementation of changelog for svnexe does ignore any file or list of files provided in the scm file set for the change log command.

I would like to provide the functionality at least for a single file. Cause i do not really see the necessity to have this also for multiple files.

But the svn log command supports this so if you would like me to go the whole extra mile i would try to do that, too.

Since there is this info/log workaround i took the priority down a notch.

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**Affects:** 2.0.1

Start by locating the svnexe provider's changelog implementation and how the SCM file set is passed to the changelog command. Compare its behavior with the svn log command's file handling. Done means changelog can retrieve the latest commit comment for at least a single specified file, with coverage for that case.

Written by the indexing model from the issue text.