Remove support for prefix-compression on row-store internal pages.

Ref #592.
Rework the WT_REF structure child page key to support on-page keys for
row-store internal pages by storing an offset/len pair in the same space
we're currently using to store the WT_IKEY reference.  Use the bottom
bit of the offset to flag which we're looking at (it's magic and will
only work on little-endian systems, add a run-time test to ensure that
is the case).  This commit doesn't actually use that new functionality,
it always instantiates internal page keys in WT_IKEY structures.

Ref #592.
Change the row-store internal page-in function to use the new page/offset
code.

Ref #592.
Turn off Huffman encoding for keys on row-store internal pages.
Ref #592.
__wt_row_key_copy is only called on row-store leaf pages -- make that
clear in the name, and quit looking at the page-type when calling the
inline cell decoding functions, we know what kind of page it is.
Ref #592.
Split __rec_cell_build_key into internal- and leaf-page versions, now
that we're not prefix compressing or Huffman encoding internal page
keys, there's a lot less work that needs to be done.

Ref #592.
It's a lot more interesting when internal pages have overflow keys than
when leaf pages do.  Split the statistic into two parts.

Ref #592.
The major/minor version support was written in a way where it wasn't
possible to drop support for a lower-numbered version.  Rework it so
support is for anything between the lowest major/minor pair to the
largest major/minor pair.

Increment the minor number, we're changing the format and we're not
supporting the previous format.

Ref #592.
If config is NULL, we're losing the version major/minor configuration
because it's preceded by a NULL in the list, this bug was hidden by the
fact that we returned version-OK for any version less than the maximum
major/minor version supported.
update the file_extend configuration semantics to match the current
pattern.
final minor stylistic cleanups, no real change.
Ref #592.
Merge branch 'develop' into branch592
Track how many bytes we skip in each lexical comparison and don't check
prefix bytes we know will match on leaf pages, not just internal pages.

Add a comment to try and explain what's going on with skiphigh/skiplow.

Reference #595.
Merge branch 'develop' into branch592

Conflicts:
	src/btree/row_srch.c
Enhance a comment.
Alex & Sue agree uint32_t is a better choice than int.
typo in a comment.
Replace the WT_REF key union's on-page key structure with a uint64_t,
then use shift operations to pull it apart.   This removes the
little-endian requirement from this part of the system and allows us to
rely less on how the compiler lays out structures.  (I'm leaving the
little-endian check I added in place, there are some other things we'd
have to fix to fully support big-endian systems.)

Ref #594.
Merge pull request #594 from wiredtiger/branch592

Reference on-page internal keys instead of copying them to allocated memory.