[dev] [dmenu] bugs and senselessness

Hey,

The last dmenu revision doesn't make any sense. It goes through a load
of hassle and complexity dynamically reallocating memory, and then has
no real effect, because text is a fixed 4096 byte buffer. Items longer
than 4096 chars are just plain inaccessible.

There are two options here. Either at the end of readstdin we can
"text = malloc(max)", and then pass around "max" instead of just using
"sizeof text" (since pointers don't work in the same way as arrays)...
which seems ugly to me... Or we can just use a 4096 byte buf in
readstdin, which makes a lot of sense anyway.

I've been working on a patch since before the recent commits anyway,
so I've merged in the ^A and ^E keybindings, but just increased the
size of the readstdin buf to sizeof text. If we *really* want dynamic
allocation and to pass around a "max" value etc, I suppose I could
merge that in instead, but I don't see the necessity: do we honestly
need to add such complexity in order to support lines longer than
4096? Those are pretty epic line lengths for what is essentially a
menu.

So the following patch fixes some bugs and oddities separate to the
whole dynamic alloc issue, as well as just increasing buf to sizeof
text, basically doing the same job as the previous revision.

Thanks,
cls