This option, when added via
  TESTS_ENVIRONMENT = [...] $(top_builddir)/run --test
allows us to run the tests and only print the full output (including
debugging etc) when the test fails.

FUSE is not very reliable on RHEL 5.

RHEL 5-era autoconf did not define these, so define them manually
when they are missing.

Define builddir as '.'  The scripts require this.  It won't work
in the srcdir != builddir case, but we don't care about that for
RHEL 5.

This commit also moves the builddir / abs_srcdir variable setting
above the include of subdir-rules.mk, in case that include uses
these variables.

Useful script:

  for f in $(find -name Makefile.am | xargs fgrep '$(abs_srcdir)' -l) ; do
    if ! grep -q '^abs_srcdir' $f; then
      echo missing in $f
    fi
  done

The first parameter (not used) is a unit, so declare it properly.

Fix typos spotted by http://github.com/lyda/misspell-check.
* configure.ac: As above.
* ocaml/examples/guestfs-ocaml.pod: Likewise.
* fish/guestfish.pod: Likewise.

On the new faster computer, Thread.yield wasn't yielding, so the
second thread would block the main test from proceeding (only when run
under valgrind however).

On the Koji builder that has lots of memory, this was trying to run
something like 20 threads.

Analyze all uses of 'int' in the code, and replace with 'size_t' where
appropriate.