VCS[git]: Environment settings.

Make GitClient::synchronousGit use the process environment.

Windows: Add a setting to fake a 'HOME' environment variable
(%HOMEDRIVE%%HOMEPATH%) to make msysgit look for its SSH-keys
there not only when run from git bash, but also from Qt Creator.
Useful in MinGw-setups, where git must not be in the path.

src/plugins/git/gitsettings.h

@@ -60,6 +60,7 @@ struct GitSettings
     bool omitAnnotationDate;
     bool spaceIgnorantBlame;
     bool diffPatience;
+    bool winSetHomeEnvironment;
     QString gitkOptions;
 };