limit of length of a single line, otherwise urxvt slows down substantial...

...ly

When you do things like this:
perl -e 'while(1) { $|=1; $i++; $c=int($i/1000); print " \t$c "; }'

you will see that urxvt slows down dramatically if url-select is included.
This patch limits the single line length to search for urls. With this it still stays fast.