Don't check parallel global length if unsafe

Just one more thing we can shave off if --unsafe is specified.
Remove unnecessary comment
Protect against unexpected %'s in printf

Scripts like printf "$foo" will choke if $foo contained unexpected %'s.
In most cases the format string obviously cannot contain %, but some of
them are not so.  This commit fixes those uses of printf.
Add acknowledgment section in intro.doc
Revive short output in crunchperf

The change in

0162ece * Fix incompatibilities with 3.12 in perf utils

made the output fatter, and the tab widths too narrow.  This change
refactors crunchperf and resurrects the output format with two digits
after each decimal point.
Fix typos in comments
Remove redundant error message