try vte.spawn_sync() if vte.fork_command_full() is missing

fork_command_full() was replaced by spawn_sync(), so if
fork_command_full() doesn't exists try to use spawn_sync()
instead.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
don't crash if vte.set_word_chars() isn't available

VTE 2.91 doesn't have a replacement for set_word_chars(),
so ignore missing function and try to continue.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Try to use RGBA as arguments to vte.set_colors if it fails with Gdk.Color

Since VTE 2.91 vte.set_colors() takes RGBA as a color, so try use it if it fails with Gdk.Color

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
make transparent background work with VTE 2.91

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Merge pull request #68 from imammedo/vte291_fixes_v2

Vte291 fixes v2