* src/vteapp.c: add options for exercising the cursor and highlight colors.
* src/debug.c: flush output streams when we check if debugging is enabled,
	because we'll probably output a string next.
* src/iso2022.c: don't print a zero-length string.  Yay compiler warnings.
* src/interpret.c: use g_print() instead of fprintf() to print.
* src/keymap.c,src/ssfe.c: include <stdarg.h>, hopefully fixing bug #121880
	(or not).