Don't hide privilege drops inside readpw() and actually make it
configurable what you are dropping to in config.h.
The privilege drop comes after opening the Display because the
user "nobody" with "nogroup" can't do that.
So why do I call this strategy the Polyphemus-Mitigation?
"""
After the giant returns in the evening and eats two more of the men,
Odysseus offers Polyphemus some strong and undiluted wine given to him
earlier on his journey. Drunk and unwary, the giant asks Odysseus his
name, promising him a guest-gift if he answers. Odysseus tells him
"Οὖτις", which means "nobody" and Polyphemus promises to eat this
"Nobody" last of all. With that, he falls into a drunken sleep. Odysseus
had meanwhile hardened a wooden stake in the fire and now drives it into
Polyphemus' eye. When Polyphemus shouts for help from his fellow giants,
saying that "Nobody" has hurt him, they think Polyphemus is being
afflicted by divine power and recommend prayer as the answer.
"""
(source: https://en.wikipedia.org/wiki/Polyphemus)
- Adds another color in config.def.h, COLOR_INIT
- Renames the colours from numerical ones to ones with meaningful names;
COLOR_INPUT for when there is content in the input buffer and COLOR_EMPTY
for when the input buffer has been cleared (backspaced or a failed attempt).
- Ensures XFreeColors frees the right number of colours. This is now derived
from the size of `Lock->colors` rather than being an integer literal.
- Makes slock exhibit the behaviour described by Markus
The default colours are the same as the ones slock currently uses, with the
exception of the new color, which I have set to red, as it indicates someone
has either failed an attempt to unlock, or that they have entered input and
erased it all.
