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
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.