Catch the standard Unix SIGTERM kill signal and do a graceful shutdown of PyBitmessage.

We already do this for the SIGINT kill signal. The change allows us to do a clean
shutdown of PyBitmessage when its process has been separated from the terminal.
#708 : Use default locale encoding

Use locale endoding else this generate error in GU : as default time format can have non ascii char on non english locale, but using ascii in locale can generate UnicodeDecodeError: 'ascii' codec can't decode byte 0xc3 :

In PyBitmessage/src/bitmessageqt/__init__.py"
    l10n.formatTimestamp())

In PyBitmessage/src/l10n.py", line 81, in formatTimestamp
    return unicode(timestring, encoding)
Merge pull request #710 from khertan/patch-1

#708 : Use default locale encoding
Increment version number to 0.4.3
Merge pull request #712 from fanquake/patch-1

Increment version number to 0.4.3
Merge pull request #709 from JonathanCoe/master

Catch the standard Unix SIGTERM kill signal and do a graceful shutdown
resolve minor merge conflict with master