Add a hidden pref to allow executing text which was sent to the terminal directly, i.e. do not strip trailing newline characters.
Also fix the stripping of trailing newline characters if there was more than one.

git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@4456 ea778897-0a13-0410-b9d1-a72fbfd435f5