Compiler clean-up and fixed issues on FreeBSD

This version of startpar introduces two fixes.

1. Suppress/avoid warnings and keep going on FreeBSD when /proc filesystem is not available.

2. Fix compiler error with GCC 15 which prevents use of internal "boolean" type. Patch provided by Mark Hindley.

0.66 - Update to documentation

The 0.66 version of startpar contains no new code or features. This release cleans up documentation in the manual page.

Make startpar testsuite more flexible

• Make sure startpar testsuite can find insserv
  executable in /usr/sbin or /sbin.

• Added PREFIX variable to Makefile and testsuite to
  make location of startpar and insserv more flexible.