regressions/ck_queue: Add coverage for previous regression.
build: Various improvements to configure script.

Add explicit detection of clang, prefer SUNCC detection over
GCC and also add support for out of source builds.
build: Support all *=* forms.
ck_ht: Enable aggressive re-use of tombstones.

Previously, a probe to an empty slot was necessary in order
to avoid hash table growth. As long as a tombstone is available,
re-use it. This prevents excessive growth on workloads involving
long bursts of writes (near 0.5 load factor) followed by long
bursts of deletes.
ck_ht: Remember to set cursor to NULL on probe end.
ck_ht: Return snapshot of object IFF we are not at end of probe sequence.
ck_ht: Set previous entry to empty on tombstone insert.
ck_ht: Increment n_entries on empty and tombstone insertions.
ck_hs: Re-use tombstones near load factor.

This is similar to the set of changes done to ck_ht.
In addition to this, a bug was caught were minimal
probe sequence was based on last rather than first
tombstone observed.

This hashset will now face long-running bursty
write -> delete -> write workloads much more effectively
and includes significant performance improvements for
delete heavy workloads (at least 2x measured).
build: Out-of-source builds for primary CK distribution.

Out of source regressions target still needs additional work
(because it's not there).
build: Remove debug left-over.
build: Disclaimer that regressions are unsupported for out-of-source builds.
build: Differentiate out-of-source builds for regressions.
build: Add out-of-source archive support.
git: Ignore additional files.
build: Bump version for next release.
build: Re-order BUILD_DIR/SRC_DIR output.
build: Prefer sed over expr for value expansion.
build: Fix typo.
build: Install ck_md.h to correct path.