Revert to previous modifier for creating rectangular selections

This is the default since forever, so don't change it on the users,
no matter what is the new default in Scintilla 3.10.0.

Fixes #2010.

src/editor.c

@@ -4936,6 +4936,9 @@ static ScintillaObject *create_new_sci(GeanyEditor *editor)
 	/* necessary for column mode editing, implemented in Scintilla since 2.0 */
 	SSM(sci, SCI_SETADDITIONALSELECTIONTYPING, 1, 0);
 
+	/* rectangular selection modifier for creating rectangular selections with the mouse */
+	SSM(sci, SCI_SETRECTANGULARSELECTIONMODIFIER, SCMOD_CTRL, 0);
+
 	/* virtual space */
 	SSM(sci, SCI_SETVIRTUALSPACEOPTIONS, editor_prefs.show_virtual_space, 0);