Fixes some regressions introduced in r5056. Losing window focus caused key modifiers to be left in an incorrect state.  Special handling of AltGr key was being applied in cases where CTRL_L+ALT_L keys were depressed which also caused the modifiers to be left in an incorrect state.  Corrected mapping of CTRL+ALT+SHIFT hotkeys to match F8 menu.

git-svn-id: https://tigervnc.svn.sourceforge.net/svnroot/tigervnc@5058 3789f03b-4d11-0410-bbf8-ca57d06f2519