doc fixes. use the older alternate-screen decset value. fixup screwups on
* src/vte.h: doc fixes. * src/dumpkeys.c: use the older alternate-screen decset value. * src/vte.c: fixup screwups on extending selection.
* src/vte.h: doc fixes. * src/dumpkeys.c: use the older alternate-screen decset value. * src/vte.c: fixup screwups on extending selection.