quick cancel: allow cancelling by key press in addition to mouse movement ref. #11

simplify post-lock cmd and die if it fails

this patch does two things:

0. simplify the code by using posix_spawn()
1. unify the behavior of what happens if the post-lock cmd fails.

currently, if `fork()` fails, slock will die without locking the screen.
HOWEVER if `execvp()` fails it prints a message to stderr (which the
user cannot see since the screen has been locked already) and only exits
the child while the parent locks the screen.

to reproduce:

	# slock some_bin_that_doesnt_exist

this behavior is inconsistent, if the idea is that post-lock cmd is
_not_ important then we shouldn't `die()` on `fork()` failure either.
and if we assume that the post-lock cmd _is_ important, then we should
die on exec failure as well.

this patch assumes the latter and calls `die()` if `posix_spawn()`
fails.

ref.
https://git.suckless.org/slock/commit/a70d5d2429abf8dcb70a8817990975dc9a621d27.html

write version to stdout like the man page says

ref.
https://git.suckless.org/slock/commit/e8bca65d629a4faa89439c9f0e599efb5a259573.html

Merge pull request #8 from herrwusel/pam_consistant

Consistent unlock styles with pam and blur patches

Consistent unlock styles with pam and blur patches

Adding background image patch

Proposed change to avoid high CPU usage ref. #7

Fix for secret password patch compilation error ref. #6

Adding dwmlogo patch ref. #5

Adding auto-timeout patch

Adding secret password patch

Adding failure-command patch

Adding color message patch ref. #3

Adding alpha patch

Adding blur pixelated screen patch

Adding keypress_feedback patch

Fix bug in DPMS patch + moved patches.h to patches.def.h to match that of config

Adding xresources patch

Added capscolor, control clear, dpms, mediakeys, message, pam auth, quickcancel patches

Properly clear the last entered character

When enter is pressed, passwd[len] will be set to '\0'. Pressing
backspace is supposed to remove the last entered character.

But currently, the clearing has an off-by-one, as in setting
passwd[len] to '\0' just like enter would do.

You can also verify it by imagining len=1 and that it's impossible to
clear passwd[0] by pressing backspace with the current code.

Signed-off-by: Tobias Stoeckmann <tobias@stoeckmann.org>