Added warning message dialog, united dialogs_show_info() and dialogs_show_error() to dialogs_show_msgbox().
Added warning message when opening files that cannot be handled correctly and set them to read-only mode.


git-svn-id: https://geany.svn.sourceforge.net/svnroot/geany/trunk@930 ea778897-0a13-0410-b9d1-a72fbfd435f5