pty: Change vte version variable name

Use "VTE_VERSION". Adapt the vte.sh script accordingly.
(cherry picked from commit 68046665721bbd36fe8035fe51ab138e9dd3c1dd)
prompt: Simplify test
(cherry picked from commit 17841f18c480c7198463b2969e9fe178a87e6632)
prompt: Fix test
(cherry picked from commit 9979712a1b556e0ddd3bf57b3ec8379b57cf66c1)

Conflicts:
	src/test-vte-sh.sh