since we may want to spawn other programs, mark every file descriptor as cloexec. Fortunately, we don't end up opening many of them!

The `page' command fetches a file and displays it using less(1). To do this, refactor fetch_fid to accept a file descriptor and add a spawn utility function.

when a tailq is proprerly initialized, there's no need to check if it's empty and insert in head position.

Drop the IMSG_AUTH_DIR imsg type and stuff everything in a struct kd_auth_proc that gets sent via IMSG_AUTH. Tweak the necessary bits to compile. While here also start documenting what data we send over which imsg. As an added benefit, now we're sending fixed-size messages instead of variable length strings.

the debugger is already disabled by some lisp tricks, so it's redundant. Moreover, we need a way to optionally toggle the debugger, so hardcoding the flag isn't useful at all.

I'm not proud of that hack, which is a double hack in fact, but I've already wasted too much time on this. The first hack is the PATH mangling, and the second the $$(cd ... ; pwd) to obtain an *absolute* path: for build in-tree top_builddir is just `.' which isn't really helpful after a cd.

In the *-suite.9ps files we have stuff like `include "lib.9ps"`, but when ninepscript is called from the *root* directory that include will fail. This is a workaround to allow including file relatively and allows to run the regress suite.