cups-browsed, driverless: Code clean-up for code of the utilities

cups-browsed, driverless: Code clean-up for code of the utilities

Cleaned up the code in the utils/ drirectory following the coding
style rules in the DEVELOPING.md file of the CUPS source code.

This improves the readability of the code a lot, especially as missing
spaces got inserted in comma-separated lists ("xxx,yyy,zzz" -> "xxx,
yyy, zzz") and around operators ("x=a*(b+c)%4" -> "x = a * (b + c) %
4"), what got nearly completely missed out by several contributors.

Comments are re-formatted to use "// ..." instead of "/* ... */", like
in PAPPL, so C and C++ files get the same comment style.

Also we get rid of the mix of many different coding styles which came
together from the many code contributions received during more than a
decade, even before the start of the cups-filters project.

In addition, all the file's header comments reflect the new license,
Apache 2.0, the same license as used for CUPS.

Note that we did not clean up driverless.c, as here we still accept a
major code contribution from the GSoC.