patch 9.0.0774: the libvterm code is outdated

Problem:    The libvterm code is outdated.
Solution:   Include libvterm changes from revision 802 to 817.  Revert some
            changes made for C89.
diff --git a/src/libvterm/Makefile b/src/libvterm/Makefile
index 2f83e0d..ba4a315 100644
--- a/src/libvterm/Makefile
+++ b/src/libvterm/Makefile
@@ -37,7 +37,7 @@
 HFILES_INT=$(sort $(wildcard src/*.h)) $(HFILES)
 
 VERSION_MAJOR=0
-VERSION_MINOR=2
+VERSION_MINOR=3
 
 VERSION_CURRENT=0
 VERSION_REVISION=0