libexec is a common path which is understood by autotools, and should be honoured. Patch from Christian "naddy" Weisgerber

This adds the capability to compile got-portable on FreeBSD.

When installing man pages, split out .1 and .5 as they install to different paths.

Rather than having a toplevel EXTRA_DIST target in the toplevel Makefile.am file, move the relevant files to their own Makefile.am locations.

The got_lib_privsep.h header expects the path to the libexec directory to be called GOT_LIBEXECDIR. At the moment it always falls back to using /usr/libexec. Fix what looks to be a typo.

This commit modifies the GoT main branch to be able to compile it under linux.