RFR: WIP: 108: Command line tools fon't run with Cygwin git

[Kevin Rushforth]

This is a very preliminary "proof of concept" patch that allows `git jcheck` to work with git from Cygwin. It is incomplete, and is missing the necessary checks to allow it to continue working with native Windows git.

@edvbld @rwestberg - I submitted it this early to get your high-level feedback on whether this support is something that you have already thought about already; if not, I'd like your feedback on the approach.

The idea would be to check whether we are are using a Cygwin version of git (this should be trivial), and if so, do the conversion between the `Path` strings and the input/output to the `git` command in all of the necessary places in `GitRepository` (that should be the only class that needs to be modified).

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Commits:
 - 11270d33: WIP: 108: Command line tools fon't run with Cygwin git

Changes: https://git.openjdk.java.net/skara/pull/170/files
 Webrev: https://webrevs.openjdk.java.net/skara/170/webrev.00
  Stats: 30 lines in 2 files changed: 23 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/skara/pull/170.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/170/head:pull/170

PR: https://git.openjdk.java.net/skara/pull/170