Do not clear variable containing submit repository. Fix potential
crash (closing diff editor before command termination),
use proper temp file name. Pass --non-interactive to "commit"
to suppress editors being launched (despite -l).

Reviewed-by: Marco Bubke <marco.bubke@nokia.com>
Task-number: QTCREATORBUG-1503

as it breaks the log output.
Task-number: QTCREATORBUG-1623

- Use message boxes on timeouts.
- Add a configuration for a graphical SSH password prompt binary with
defaults
- Launch commands that require authentification with no terminal on UNIX
and environment variable SSH_ASKPASS set accordingly.
- First attempt at introduce a common function to synchronously run VCS
commands in base plugin with flags.
- Use standard execution log entries in all VCS plugins (outputwindow).

- git status: Recognize text in case -u was passed
- Mercurial: Always run in C locale

Introduce static utilities to Utils::SynchronousProcess
for synchronous processes that mimicks the handling
of Utils::SynchronousProcess (apply timeout after no
more data are available on stdout/stderr as opposed
to waitForFinished()).

Task-number: QTCREATORBUG-777

Add a QVariant cookie to HgTask to be emitted on successful
execution, wired to IVersionControl.

Start the jobrunner on demand, save options only if changed,
give it the structure used elsewhere in the VCS plugins. Remove
last traces of the cmd /c hack.

Do not use "cmd /c hg" on Windows as this will fail randomly
depending on arguments with blanks, such as "-U 8". Output log
messages about synchronous commands, format author correctly,
label menus correctly.

Polish: Canconical slots, const-correctness, some QLatin1Strings/tr,