Perforce: Use new VCSBasePlugin class.

Use relative paths with -d-option, check for symlinked depots.
Add revert-actions.
Use different context/kinds for editors, suppressing warnings.
Introduce common run-function.

src/libs/utils/synchronousprocess.h

@@ -110,6 +110,9 @@ public:
     QStringList environment() const;
     void setEnvironment(const QStringList &);
 
+    void setProcessEnvironment(const QProcessEnvironment &environment);
+    QProcessEnvironment processEnvironment() const;
+
     void setWorkingDirectory(const QString &workingDirectory);
     QString workingDirectory() const;