Many tests didn't change back from subdirectories at the end of the tests ...
and they don't have to. The missing 'cd ..' could always be added when another
test case is added to the test file.
This change do that tests (99.5%) consistently end up in $TESTDIR where they
started, thus making it simpler to extend them or move them around.
Using terminfo instead of hard-coding ECMA-48 control sequences provides a
greater assurance that the terminal codes are correct for the current
terminal type; not everything supports the ANSI escape codes.
It also allows us to use a wider range of colors when a terminal emulator
supports it (such as 16- or 256-color xterm), and a few more non-color
attributes, such as the ever-popular blink.
